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Impact of different privacy conditions and incentives on survey response rate, participant representativeness, and disclosure of sensitive information: A randomized controlled trial

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Background Anonymous survey methods appear to promote greater disclosure of sensitive or stigmatizing information compared to non-anonymous methods. Higher disclosure rates have traditionally been interpreted as being more accurate than lower rates. We examined the impact of 3 increasingly private mailed survey conditions—ranging from potentially identifiable to completely anonymous—on survey response and on respondents’ representativeness of the underlying sampling frame, completeness in answering sensitive survey items, and disclosure of sensitive information. We also examined the impact of 2 incentives ($10 versus $20) on these outcomes. Methods A 3X2 factorial, randomized controlled trial of 324 representatively selected, male Gulf War I era veterans who had applied for United States Department of Veterans Affairs (VA) disability benefits. Men were asked about past sexual assault experiences, childhood abuse, combat, other traumas, mental health symptoms, and sexual orientation. We used a novel technique, the pre-merged questionnaire, to link anonymous responses to administrative data. Results Response rates ranged from 56.0% to 63.3% across privacy conditions (p = 0.49) and from 52.8% to 68.1% across incentives (p = 0.007). Respondents’ characteristics differed by privacy and by incentive assignments, with completely anonymous respondents and $20 respondents appearing least different from their non-respondent counterparts. Survey completeness did not differ by privacy or by incentive. No clear pattern of disclosing sensitive information by privacy condition or by incentive emerged. For example, although all respondents came from the same sampling frame, estimates of sexual abuse ranged from 13.6% to 33.3% across privacy conditions, with the highest estimate coming from the intermediate privacy condition (p = 0.007). Conclusion Greater privacy and larger incentives do not necessarily result in higher disclosure rates of sensitive information than lesser privacy and lower incentives. Furthermore, disclosure of sensitive or stigmatizing information under differing privacy conditions may have less to do with promoting or impeding participants’ “honesty” or “accuracy” than with selectively recruiting or attracting subpopulations that are higher or lower in such experiences. Pre-merged questionnaires bypassed many historical limitations of anonymous surveys and hold promise for exploring non-response issues in future research.
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R E S E A R C H A R T I C L E Open Access
Impact of different privacy conditions and
incentives on survey response rate, participant
representativeness, and disclosure of sensitive
information: a randomized controlled trial
Maureen Murdoch
1,2,3*
, Alisha Baines Simon
2
, Melissa Anderson Polusny
2,4,5
, Ann Kay Bangerter
2
,
Joseph Patrick Grill
2
, Siamak Noorbaloochi
2,3
and Melissa Ruth Partin
2,3
Abstract
Background: Anonymous survey methods appear to promote greater disclosure of sensitive or stigmatizing
information compared to non-anonymous methods. Higher disclosure rates have traditionally been interpreted
as being more accurate than lower rates. We examined the impact of 3 increasingly private mailed survey
conditionsranging from potentially identifiable to completely anonymouson survey response and on
respondentsrepresentativeness of the underlying sampling frame, completeness in answering sensitive survey items,
and disclosure of sensitive information. We also examined the impact of 2 incentives ($10 versus $20) on these outcomes.
Methods: A 3X2 factorial, randomized controlled trial of 324 representatively selected, male Gulf War I era veterans who
had applied for United States Department of Veterans Affairs (VA) disability benefits. Men were asked about past sexual
assault experiences, childhood abuse, combat, other traumas, mental health symptoms, and sexual orientation. We used a
novel technique, the pre-merged questionnaire, to link anonymous responses to administrative data.
Results: Response rates ranged from 56.0% to 63.3% across privacy conditions (p= 0.49) and from 52.8% to 68.1% across
incentives (p= 0.007). Respondentscharacteristics differed by privacy and by incentive assignments, with completely
anonymous respondents and $20 respondents appearing least different from their non-respondent counterparts.
Survey completeness did not differ by privacy or by incentive. No clear pattern of disclosing sensitive
information by privacy condition or by incentive emerged. For example, although all respondents came from the same
sampling frame, estimates of sexual abuse ranged from 13.6% to 33.3% across privacy conditions, with the highest
estimate coming from the intermediate privacy condition (p=0.007).
Conclusion: Greater privacy and larger incentives do not necessarily result in higher disclosure rates of sensitive
information than lesser privacy and lower incentives. Furthermore, disclosure of sensitive or stigmatizing information
under differing privacy conditions may have less to do with promoting or impeding participants’“honestyor
accuracythan with selectively recruiting or attracting subpopulations that are higher or lower in such experiences.
Pre-merged questionnaires bypassed many historical limitations of anonymous surveys and hold promise for exploring
non-response issues in future research.
Keywords: Randomized trial, Patient surveys, Participation bias, Non-response bias, Anonymity, Confidentiality
* Correspondence: Maureen.Murdoch@va.gov
1
Section of General Internal Medicine, Minneapolis VA Medical Center,
Minneapolis, MN, USA
2
Center for Chronic Disease Outcomes Research, Minneapolis VA Medical,
One Veterans Drive, Minneapolis, MN 55417, USA
Full list of author information is available at the end of the article
© 2014 Murdoch et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative
Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain
Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article,
unless otherwise stated.
Murdoch et al. BMC Medical Research Methodology 2014, 14:90
http://www.biomedcentral.com/1471-2288/14/90
Background
Surveys represent one of the most efficient and inexpen-
sive research methods available to collect representative,
high quality data from large numbers of research partici-
pants. They therefore frequently serve as the backbone
used to define the scope and magnitude of many poten-
tial public health problems. In the United States, for ex-
ample, large national surveys have been used to estimate
what proved at the time to be surprisingly high levels of
mental illness within the general population [1], physical
violence within families [2], and sexual assault among
women [3]. Even the United States Census, which serves
as the basis of apportioning Congressional representatives
and taxes to each state, is survey-based. Typically, survey
data are either collected by interviewers using face-to-face
or telephone communication with the participant or via
the participants own self-report.
Regardless of the topic studied and how the information
is collected, scientifically correct, survey-based prevalence
estimates require that research participants be representa-
tive of the population from which they are drawn, that
participants actually answer the questions that are asked
of them, and that they answer those questions honestly.
On average, research participants disclose sensitive and
personal information, such as mental health symptoms,
drug misuse, and history of sexual assault more fre-
quently when responding to self-administered question-
naires than when taking part in face-to-face or telephone
interviews [4-7]. Studies suggest that disclosure of sensi-
tive information on self-administered questionnaires is
enhanced yet more when participants respond anonym-
ously instead of confidentially [5,8-11]. This implies
that anonymous, self-administered surveys may be the
optimal method for accurately cataloging information
about certain public health problems, such as the preva-
lence of physical or sexual abuse or of mental health
symptoms.
Although by no means proven, most survey researchers
take the stance that methods that generate higher preva-
lence estimates for stigmatizing or sensitive information
are probably more accurate than methods that generate
lower estimates. This stance, however, rests upon a rather
unlikely assumption that all people carry the same pro-
pensity to participate in survey research. Particularly when
a survey topic is sensitive, survey respondents tend to dif-
fer substantially from non-respondents [12]. Therefore,
three mechanisms might explain why anonymous surveys
generate higher prevalence estimates of stigmatizing or
sensitive information compared to non-anonymous sur-
veys: 1) propensity to participate in research is in fact
equal across all members of a sampling frame, and an-
onymous methods promote more honest self-disclosure
among the participants with stigmatizing experiences;
2) sampling frame members with stigmatizing experiences
are more reluctant than others to participate in surveys,
but anonymous methods reduce this inherent reluc-
tance (under selection is reduced); 3) anonymous methods
disproportionately increase the propensity of people with
stigmatizing experiences to participate in the survey rela-
tive to those without such experiences (over selection
is induced). The first two mechanisms reduce bias; the
last introduces bias. Without information about non-
respondentscharacteristics relative to respondents,how-
ever, one cannot determine which possibility is correct.
Unfortunately, under typical anonymous conditions, such
information is unavailable.
Anonymous surveys carry other drawbacks relative to
confidential surveys. For example, unlike confidential
survey methods, anonymous survey responses cannot be
linked to administrative or other non-survey data, thus
limiting anonymous datas richness and utility. Also, un-
less creative methods are employed, researchers often can-
not track or send follow-up mailings to non-respondents
of anonymous surveys, thus obtaining inferior response
rates (e.g., [13]). While low response rates do not neces-
sarily correlate to poor data quality, risks for non-response
bias do increase with lower response rates.
Two methods to bypass the tracking limitation in an-
onymous surveys have been described. In one, partici-
pants return a completed survey and a separately mailed
postcard. Only the postcard contains a unique identifier,
which is used to track respondents [14-16]. However,
this method increases respondent burden, which can re-
duce response rates. Furthermore, participants may find it
confusing and hence return only one item e.g., the sur-
vey or the postcard, but not both. Receipt of equal num-
bers of postcards and surveys do not necessarily mean the
same people returned both. Even when both are returned
by the same person, the survey may be received consider-
ably earlier than the postcard. The participant may there-
fore be subjected to additional mailings until the postcard
is received, which may be annoying, and the researcher
may incur unnecessary mailing expenses. Finally, unbe-
knownst to the researcher, some respondents may return
more than one survey, leading to the overweighting of
those individualsresponses.
A second approach uses tracking envelopes, which sim-
plifies respondent burden, circumvents the problem of
postcards and surveys returning at different times, and
avoids analyzing multiple responses from a single partici-
pant [17]. In this approach, the envelope contains a unique
identifier, but not the survey. The two are returned to-
gether but separated immediately upon opening. Received
surveys are then intermixed in some random fashion to
avoid any possibility of linking them back to their ori-
ginal envelopes. If one participant returns more than
one envelope-survey pair, all but the first is discarded.
Until the envelope and survey are separated, however,
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thesurveyisnottrulyanonymous.Participantsmust
rely on the researchers integrity to maintain anonymity,
and they may be less willing to disclose sensitive informa-
tion relative to the postcard tracking method, where priv-
acy is absolute. Each approach has pros and cons, but the
twos effect on response rates, survey completeness, or dis-
closure of sensitive information have never been directly
compared.
In the present paper we address these issues using a
novel technique we developed, the pre-merged question-
naire, which allows comparisons between respondents
and non-respondents even under anonymous survey
conditions. The study involved a potentially sensitive,
self-administered questionnaire asking about several
traumatic experiences, including sexual assault during
military service. The population of interest was male US
Gulf War I era veterans with possible posttraumatic
stress disorder (PTSD) who had previously applied for
Department of Veterans Affairs (VA) disability benefits.
We had reason to believe that sexual assault experiences
were particularly high in this population [18]. However,
we also feared that traditional rape myth beliefs [19],
which may be especially strongly held by military ser-
vice members socialized into a masculinized subcul-
ture, might either deter male sexual assault survivors
participation in the research or impede their disclos-
ing of such experiences.
Using 3 levels of increasing privacy tied to the tracking
methods described above, we hypothesized that re-
sponse rate and participant representativeness, the
number of sensitive questions actually answered by
participants, and the proportion of participants disclos-
ing potentially sensitive information would increase in
a dose-response manner from the lowest to highest priv-
acy condition. Because higher incentives consistently
improve survey response [20], we also tested the im-
pact of two incentives, $10 versus $20, on survey re-
sponse. We expected the response rate, number of
sensitive questions answered, and proportion of par-
ticipants disclosing sensitive information would be
higher among those receiving the $20 incentive com-
pared to the $10 incentive.
Methods
Population and setting
We used simple randomization without replacement to
select 324 veterans for survey from the population of
46,824 men who applied for VA PTSD disability benefits
prior to June 2007 and had served in the US Armed
Forces between August 2, 1990 and July 31, 1991.
Study design and assignment
The study was a 3X2 factorial, randomized controlled
trial (Figure 1). Using simple randomization, Veterans
were assigned to one of 3 tracking/privacy condi-
tions:
1) Confidential: Under the least private condition,
veterans received a survey with a highly visible,
coded, unique identifier affixed to the front page of
the survey. This was used for tracking, and
individual respondents were potentially identifiable
from their surveys.
2) Anonymized-Envelope: Intermediate in privacy,
veterans were asked to return their surveys in a
study envelope, which had a pre-printed, unique
identification number (ID) on it. When the
completed questionnaire was returned, study
personnel immediately separated it from the
envelope. The questionnaire was intermixed with
other arriving surveys and set aside. The envelope
ID was used to indicate who had returned surveys.
Technically, as long as the survey resided within the
envelope, respondents could be identified. Thus,
this method was not fully anonymous. Once the
questionnaire was removed from the envelope,
however, there was no longer any way to identify the
respondent (hence the term anonymized).
3) Anonymous-Postcard: The most private condition,
veterans returned their surveys in unmarked
envelopes. Besides the survey, veterans were also
asked to return an enclosed, brightly colored
postcard, which had a unique ID to allow tracking.
Respondents could not be identified from their
surveys or envelopes at any time.
Once Veterans were assigned to their tracking/privacy
condition, we then used simple randomization within each
condition to assign them to receive $10 or $20.
Protocol
Data collection
For all groups, the initial mailing included a cover letter
describing the studys risks and benefits, the cash incen-
tive, and 25-page questionnaire. At two week intervals,
non-respondents were mailed a post-card reminder, a
second mailing of the survey, and a final mailing of the
survey via overnight mail (Federal Express). Cover letters
were printed on Minneapolis VA Medical Center letter-
head and listed the studys funding agency. Veterans
were told that they had been selected for survey because
they had filed a VA disability claim and had served dur-
ing Gulf War I. They were also told that the survey
would ask about combat, unwanted sexual attention,
and other lifetime and military experiences. The cover
letters also stated in bold-face font, We would like to
hear from you even if you never experienced combat or
unwanted sexual attention. We would also like to hear
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from you even if you were not deployed to the Persian
Gulf.Cover letters were the same across groups, except
that they described the incentive, tracking method, and
privacy protections that were specific to each group.
Copies of cover letters are available upon request.
Pre-merged questionnaires
To our knowledge, we are the first to develop pre-merged
questionnaires for use in anonymous surveys. However,
pre-merged questionnaires are simply an extension of the
common strategy of using different colored paper, say, to
collect data from different groups (e.g., green paper for
men, yellow for women). Instead of different colored pa-
pers, however, we created a sticker that was applied to each
subjects questionnaire just before mailing. The sticker was
designed to be as unobtrusive as possible and was thus
camouflaged as a return address on the surveys back page
(Figure 2). Just below the address, we embedded an alpha-
numeric code into the mailcode, which corresponded to
key administrative data associated with each potential
subject. When the survey was returned, so was the admin-
istrative dataalready merged. The sticker code was delib-
erately intended to be non-exclusive to the subject. For
example, a code such as 504ADBY, indicating a veteran
was aged 50 years or older, served 4 years in the Army and
received disability benefits from the VA, could apply to
hundreds of thousands of veterans.
We maintained two separate, but interrelated computer-
ized files: an administrative file containing subjectsname
and administrative codes, which were used to generate the
stickers, and a tracking file containing their names and
tracking ID. As envelopes, postcards, or confidential sur-
veys were returned, the tracking ID was entered into the
tracking file. This action deleted respondentsname and ID
from the tracking file and triggered a simultaneous deletion
of their name and administrative code from the adminis-
trative file. Thus, by studys end, only non-respondents
administrative codes remained in the computerized rec-
ord. These were then used to compare non-respondents
to respondents. Respondentsadministrative codes were
Figure 1 Study flow chart.
Figure 2 Example of a pre-merged sticker. For the present study, the sticker was placed within a pre-printed box on the last page of the survey.
In this example, administrative data begins after the Ein the Mailcode.
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recaptured from the sticker on their returned question-
naires and hand-entered back into the analytical frame.
Measures
Primary outcomes
The primary outcome was response rate, calculated as
the number of returned surveys divided by the number
of veterans assigned to each arm.
Secondary outcomes
Secondary outcomes included the representativeness of
respondents, percentage of Veterans fully completing all
sensitive survey items, and the percentage disclosing sen-
sitive information. Information collected by the survey
that we thought might be sensitive included veteransex-
periences of sexual abuse, including sexual assault during
the time of Gulf War I; other traumatic experiences, in-
cluding combat and childhood physical abuse; mental
health problems, including depression, PTSD, and prob-
lem drinking; and veteranssexual orientation.
Representativeness of respondents We used data from
the pre-merged sticker to compare respondents to non-
respondents. Available data included age greater than or
equal to 50 years versus younger, service in the Army
versus other branch, VA disability benefit status (receiv-
ing versus not), and any VA health care utilization versus
none. Specifically, we assessed whether the participant
had made a visit to any VA medical facility in the prior
year for any reason or had made visits to a VA facility
for primary or mental health care. The term, original
sample, refers to all veterans selected for the survey, re-
gardless of their response status. Responders and respon-
dents refer to the subset of veterans from the original
sample who returned surveys, and non-responders/non-
respondents refer to the subset of veterans who did not
return surveys.
Sensitive information Sensitive information was col-
lected by the survey and included the following:
Sexual abuse
We used 3 items from Sexual Harassment Inventorys
criminal sexual misconduct scale [21] plus one
additional item [22] to assess sexual assault during the
time of Gulf War I, 4 items from the Sexual Abuse
subscale of the Childhood Trauma Questionnaire [23]
to assess childhood sexual abuse, and one item from
the Life Stressor Checklist [24] to assess any sexual
assault in the past year. A positive response to any one
of these questions indicated a history of sexual abuse.
Other traumatic experiences
Other traumatic experiences included combat
exposure, assessed using an adapted Combat Exposure
Inventory [25] version; childhood physical abuse,
assessed using items from the Childhood Trauma
Questionnaires relevant subscale [23]; and past-year
traumas, assessed using an adaptation of the Life Stressor
Checklist [24]. Veterans who reported any childhood
physical abuse item more than rarelywere considered
physically abused.
Mental health problems
We used the 5-item RAND Mental Health Battery [26]
to assess depression, the Penn Inventory for PTSD [27]
to assess PTSD symptoms, and the TWEAK [28]to
assess alcohol misuse.
Sexual orientation
Sexual orientation was assessed using a single survey
item that read, People are different in their sexual
attraction to other people. Which best describes your
feelings?Responses ranged from 1=Completely
heterosexual or straight’” to 5=Completely
homosexual or gay’”. Responses were dichotomized as
Completely heterosexualversus Not completely
heterosexualfor analysis.
Power
The study was funded to examine different incentivesim-
pact on response rate and had 80% power to detect a 10%
difference in response rates across incentives, assuming a
60% response rate in the $10 group and two-tailed alpha
of 0.05.
Analysis
The study was intended to examine main effects, but in-
teractions were assessed in an exploratory fashion. Results
are reported for tracking/privacy condition first; incentive
condition second; and, when tested, interactions third. We
used χ
2
tests to compare outcomes across privacy condi-
tions and incentives and to compare respondents and
non-respondents. We used logistic regression to test for
interactions between tracking/privacy condition and
incentive on outcomes. We used IBM SPSS Statistics
(version 19) and SAS (version 9.2) statistical packages
for analyses.
Masking, disclosure, and ethical approval
Data collectors and analysts were aware of study group
assignment. The Minneapolis VA Medical Centers
Subcommittee for Human Studies approved the protocol.
Results
Response rate
Response rate overall was 60.5% and did not differ signifi-
cantly across tracking/privacy assignments (Confidential
response rate = 56.0%, Anonymized-envelope response
rate = 63.3%, Anonymous postcard response rate = 62.3%,
p= 0.49). However, the response rate was almost 15 full
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percentage points higher among veterans randomized to
receive the $20 incentive (response rate = 68.1%) com-
pared to the $10 incentive (response rate = 52.8%, p=
0.007). While the lowest response rate was obtained from
men randomized to the Confidential/$10 incentive group
(response rate = 43.6%; see Figure 1), tests for interactions
between tracking/privacy and incentives on response rate
were not statistically significant (p=0.46).
Respondent representativeness
As Table 1 shows, randomization failed to evenly distribute
the 324 veterans according to their past-year VA health
care utilization. Specifically, veterans randomized to the
Anonymous-Postcard were less likely to have made a VA
health care visit of any kind in the past year than were
veterans randomized to the Anonymized-Envelope and
Confidential groups (67.6% versus 75.4% in the other two
conditions). Otherwise, randomization successfully distrib-
uted all the remaining administrative characteristics evenly
across all the tracking/privacy and incentive conditions.
The characteristics of survey responders are shown in
Table 2. Responders in the Anonymized-Envelope group
had a higher proportion of individuals aged 50 years or
older, a lower proportion of white persons, and a lower
proportion of persons working for pay compared to the
other two groups, but none of these differences were sta-
tistically significant (all ps > 0.18). Consistent with the
original samples maldistribution, Anonymous-Postcard re-
spondents were less likely than other respondents to have
made a visit of any kind to a VA medical facility in the
prior year. Compared to the other tracking/privacy condi-
tions, Anonymous-Postcard respondents were also sub-
stantially less likely to have made a mental health care visit
to a VA medical facility, but this could not be attributed to
a maldistribution of the original sample. Compared to the
administrative record, all respondents substantially under-
reported receiving VA disability benefits.
Respondents in the $10 incentive arm were signifi-
cantly older, less likely to be working for pay, and more
likely to say they received VA disability benefits than re-
spondents in the $20 incentive arm. Both groups substan-
tially underreported their receipt of VA disability benefits
compared to the administrative record. There were no sta-
tistically significant tracking/privacy-by-incentive interac-
tions (all ps > 0.20).
Table 3 presents information for the original sample,
stratified by response status and by study assignment. Find-
ings show that Confidential and Anonymized-Envelope re-
spondents differed significantly from their non-respondent
counterparts in terms of age and service branch. Compared
to their non-respondent counterparts, Confidential re-
spondents were also more likely to be receiving VA
disability benefits, and Anonymized-Envelope respon-
dents were more likely to have made VA primary care
and mental health visits. There were significant age differ-
ences among respondents and non-respondents random-
ized to receive $10, but respondents and non-respondents
did not differ significantly on any available characteristic
among those assigned to the Anonymous-Postcard or $20
incentive. There were no significant tracking/privacy-by-
incentive interactions.
Percentage fully completing sensitive items and percentage
disclosing sensitive information
As Table 4 shows, with the exception of combat items, re-
spondents answered every item on each of the potentially
sensitive scales more than 90% of the time, regardless of
tracking/privacy condition or incentive. Twenty-six ques-
tions were used to assess combat exposure, which may
explain why it had the most skipped items (10.7% over-
all), though respondents were twice as likely to skip a
combat item as they were to skip a PTSD item (3.1% over-
all), which also contained 26 questions. The sexual abuse
questions were second most likely to be skipped (7.1%
overall). There were no statistically significant associations
between tracking/privacy assignment and completion of
sensitive survey items. Likewise, higher incentive was not
associated with greater completion of sensitive survey
Table 1 Population characteristics by tracking/privacy condition and incentive; results reported as a percentage (%)
Characteristic Overall By tracking/privacy condition Incentive
Confidential Anonymized-Envelope Anonymous-Postcard $10 $20
N= 324 n= 109 n= 109 n= 106 n= 161 n= 163
Age > =50 yrs 35.8 32.1 42.2 33.0 40.4 31.3
Army service 63.0 67.0 59.6 62.3 65.8 60.1
Receiving VA disability benefits 83.3 83.5 83.5 83.0 86.3 80.4
VA visit last yr:
Any type 74.1 76.1 80.7 65.1 77.0 71.2
Primary care 63.3 62.4 70.6 56.6 62.1 64.4
Mental health 47.5 50.5 54.1 37.7 51.6 43.6
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items, and there were no interactions between tracking/
privacy assignment and incentive.
As Table 5 shows, Anonymized-Envelope respondents
were substantially more likely than other respondents to
disclose a history of sexual abuse. Several other contrasts
appeared numerically large, even though they did not
reach statistical significance: Anonymous-Postcard respon-
dents reported more childhood physical abuse (p=0.06)
and had fewer positive depression screens compared to the
other tracking/privacy groups (p= 0.09), and Confidential
respondents reported more combat (p=0.09) and had
more positive PTSD screens (p= 0.08).
Table 2 Respondent characteristics by tracking/privacy condition and incentive, results reported as a percentage (%)
Characteristic Overall By tracking/privacy condition By incentive
Confidential Anonymized-Envelope Anonymous-Postcard $10 $20
N= 196 n=61 n=69 n=66 n=85 n= 111
Age > =50 years 44.4 42.6 50.7 39.4 56.5 35.1***
Race
White 52.6 55.7 47.8 54.5 54.1 51.4
Black 27.0 21.3 34.8 24.2 22.4 30.6
Hispanic 6.1 8.2 5.8 4.5 8.2 4.5
Some college experience 74.5 75.4 73.9 74.2 76.5 73.0
Married 67.4 67.8 65.2 69.2 66.3 68.2
Working for pay 61.0 61.0 55.2 67.2 51.9 67.3*
Served in Army 60.2 63.9 56.5 60.6 63.5 57.7
Receiving VA disability benefits:
Per the administrative record 84.2 90.2 82.6 80.3 87.1 82.0
Per self-report 68.4 75.4 71.0 59.1 76.5 62.2*
VA visit in past year:
Any type 78.1 82.0 87.0 65.2* 81.2 75.7
Primary care 67.9 67.2 79.7 56.1 68.2 67.6
Mental health 51.0 54.1 65.2 33.3*** 60.0 44.1
Bold face font signifies a statistically significant difference across group.
*p0.05, ***p0.001.
Table 3 Characteristics of original sample, stratified by response status and by tracking/privacy condition and
incentive; results reported as a percentage (%)
Characteristic Overall Overall by response By tracking/privacy condition By Incentive
Confidential Anonymized-
Envelope
Anonymous-
Postcard
$10 $20
N= 324 n= 109 n= 109 n= 106 n= 161 n= 163
Respondent? Respondent? Respondent? Respondent? Respondent? Respondent?
Yes No Yes No Yes No Yes No Yes No Yes No
N= 324 n= 196 n= 128 n=61 n=48 n=69 n=40 n=66 n=40 n=85 n=76 n= 111 n=52
Age > =50 yrs 35.8 44.4 22.7*** 42.6 18.8** 50.7 27.5* 39.4 22.5 56.5 22.4*** 35.1 23.1
Army service 63.0 60.2 67.2* 63.9 70.8* 56.5 65.0* 60.6 65.0 63.5 68.4 57.7 65.4
Receiving VA
disability
benefits 83.3 84.2 82.0 90.2 75.0* 82.6 85.0* 80.3 87.5 87.1 85.5 82.0 76.9
VA visit last yr:
Any type 74.1 78.1 68.0 82.0 68.8 87.0 70.0** 65.2 65.0 81.2 72.4 75.7 61.5
Primary care 63.3 67.9 56.2 67.2 56.2 79.7 55.0** 56.1 57.5 68.2 55.3 67.6 57.7
Mental health 47.5 51.0 42.2 54.1 45.8 65.2 35.0** 33.3 45.0 60.0 42.1 44.1 42.3
Bold face font signifies a statistically significant difference between respondents and non-respondents within that column.
*p0.05, **p0.01, ***p0.001.
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Main effects in disclosing sensitive information by in-
centive did not reach statistical significance. However,
there was a trend toward statistical significance in the pro-
portion of respondents randomized to the $10 incentive
with a positive depression screen compared to the $20
respondents (p= 0.08). Among Anonymized-Envelope re-
spondents, those randomized to the $10 incentive were
substantially more likely to screen positive for PTSD than
those in the $20 arm (90.6% v.65.8%;p=0.05). Otherwise,
there were no tracking/privacy-by-incentive interactions.
Table 4 Percentage (%) of respondents fully completing all items in a potentially sensitive scale by tracking/privacy
condition and incentive
Scale/Item Number of
items in scale
Percentage (%) completing all items in the scale
Overall By tracking/privacy condition By incentive
Confidential Anonymized-Envelope Anonymous-Postcard $10 $20
N= 196 n=61 n=69 n=66 n=85 n= 111
Sexual Orientation 1 98.5 100 98.6 95.5 97.6 98.2
Sexual Abuse 8 92.9 93.4 94.2 90.9 91.8 93.7
Other Traumatic events:
Combat
a
26 89.3 86.5 96.8 85.7 89.1 89.5
Childhood physical abuse 5 96.4 96.7 97.1 95.5 95.3 97.3
Past-year events:
Economic hardship 1 98.5 100 97.1 98.5 97.6 99.1
Emotional abuse/neglect 1 99.0 98.4 100 98.5 98.8 99.1
Crime victim 1 99.0 100 98.6 98.5 97.6 100
Physical attack 1 98.5 98.4 98.6 98.5 97.6 99.1
Mental health screens
Depression 5 99.0 100 98.6 98.5 98.8 99.1
PTSD 26 96.9 100 97.1 93.9 94.1 99.1
Problem drinking 5 100 100 100 100 100 100
a
Among those who said they experienced any combat in the Gulf.
Table 5 Percentage (%) of respondents disclosing potentially sensitive information by tracking/privacy condition and
incentive
Sensitive information disclosed Overall By tracking/privacy condition By incentive
Confidential Anonymized-Envelope Anonymous-Postcard $10 $20
N= 196 n=61 n=69 n=66 n=85 n= 111
Not completely heterosexual 7.8 11.5 4.4 7.9 7.2 8.3
Any sexual abuse ever 20.9 14.8 33.3** 13.6 16.5 24.3
Other traumatic experiences
Combat during Gulf War I 78.6 90.2 72.1 74.5 80.7 77.7
Childhood physical abuse 64.3 57.4 59.4 75.8 61.2 66.7
Past-year events:
Economic hardship 43.3 41.0 42.6 46.2 39.8 45.9
Emotional abuse/neglect 22.6 23.3 25.7 18.5 26.2 19.8
Crime victim 10.8 9.8 13.0 9.2 9.6 11.6
Physical attack 5.2 6.7 7.2 1.5 1.2 0.9
Positive mental health screens:
Depression 44.6 50.8 47.8 35.4 52.4 39.1
PTSD 79.2 85.2 77.1 75.8 83.5 75.9
Problem drinking 35.1 31.1 28.6 34.8 36.5 27.7
Bold face font signifies a statistically significant difference across groups.
**p0.01.
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Discussion
In this randomized controlled trial, more survey privacy
was not associated with statistically significantly higher re-
sponse rates compared to less privacy, nor did tracking/
privacy condition affect the proportion of respondents
who actually answered our sensitive questions. Instead,
each tracking/privacy condition attracted its own unique
pool of respondents, which in turn may have influenced
our group-specific estimates of sexual abuse, childhood
physical abuse, combat, and mental health problems
despite the fact that all participants originated from the
same sampling frame. Estimates of sexual abuse, for ex-
ample, were more than 2 times higher in the Anonymized-
Envelope condition than in the other two conditions.
As expected, the higher incentive resulted in a sub-
stantially higher response rate than the lower incentive,
but there was no association between incentive and the
proportion answering our sensitive questions. As with
the tracking/privacy manipulation, each incentive ap-
peared to attract its own unique pool of respondents, with
the larger incentive attracting younger workers for pay
who were less likely to say they were receiving disability
benefits compared to the smaller incentive. Statistically,
prevalence estimates for potentially sensitive or stigmatiz-
ing material did not differ significantly by incentive, des-
pite some numerically large differences. For example,
more than half of respondents randomized to the $10 in-
centive screened positive for depression, compared to
about a third of respondents in the $20 arm.
According to leverage-salience theory [29], individuals
attend to different criteria when deciding to return a sur-
vey and, further, assign to each criterion different weights
and importance. These are known as leverages.Inthe
present study, each tracking/privacy and incentive condi-
tion appeared to trigger a different set of leverages, so that
unique subpopulations selectively participated in each of
the studys arms. When considering sensitive material,
therefore, one cannot assume that the survey method gen-
erating the highest estimate is most accurate.
Since Anonymous-Postcard respondents did not differ
significantly from non-respondents on available measures,
one might be tempted to conclude that this tracking/
privacy method generated the most representative sample of
respondents and hence most accurate prevalence estimates. If
so, one would also have to conclude that the Anonymized-
Envelope approach over recruited sexual abuse survivors. His-
tory of sexual abuse was 13.6% among Anonymous-Postcard
respondents and 33.3% among Anonymized-Envelope re-
spondents. However, we have shown elsewhere that, even
when using Anonymized-Envelopes, survey respondents
underreport their military sexual assault experiences by a
factor of three [30]. This suggests that the Anonymized-
Envelope method either reduces under selection of veterans
with sexual abuse histories or optimizes more honest
reporting among those who have such historiesor both
compared to the Anonymous-Postcard method. It may do
so,however,attheexpenseofeitheroverexcludingvet-
erans with a history of childhood physical abuse or discour-
aging honestreporting of childhood abuse. In the present
study the Anonymized-Envelope method generated a sub-
stantially lower, albeit not statistically significant, estimate
of childhood physical abuse of 59.4% compared to the
Anonymous-Postcards estimate of 75.8%.
In general, tracking/privacy condition and incentive
level appeared to affect respondent representativeness in-
dependently, with incentivesprincipal impact being the
recruitment of younger and healthier participants. These
findings may be reassuring to Human Studies oversight
boards, who might otherwise worry that large incentives
coerce the sickest and most vulnerable into survey re-
search participation. Halpern et al. [31] has shown that
higher payment levels do not override research partici-
pantsrisk perceptions when considering whether to en-
roll in clinical trials, and, furthermore, poorer, presumably
more vulnerable participants are actually less sensitive to
higher incentive levels than are wealthier participants.
Similar findings have been reported for those deciding
whether to respond to a survey [32].
The present study offers proof-of-concept for pre-merged
questionnairesutility. However, pre-merged question-
naires will prove most powerful when they incorporate ad-
ministrative information that is highly related to the
surveys topic (e.g., sexual abuse, childhood abuse) instead
of basic demographic information. Because we did not
have such information for the present study, we cannot
say whether our differing estimates for these sensitive data
across the three tracking/privacy conditions were a func-
tion of reducing or inflating selection biases, a function of
enhancing or impeding honestreporting, or both. Future
research will be needed to explore these issues further. It
may well be that different tracking/privacy methods will
prove best for different sensitive topics.
We used a computerized system to manage the track-
ing and administrative data interface in the present
study, but the pre-merged questionnaire concept could
easily be applied to manual methods. For example in a
study using up to three survey mailings per subject, one
could pre-print 3 stickers per subject, file them under
each subjects name, and then throw away any remaining
stickers once the subjects postcard or envelope ID was
returned. By studys end, only non-respondentsstickers
would remain.
Pre-merged questionnaires carry important limitations.
Researchers must be selective in what data they encode
to keep the sticker from becoming uniquely identifying.
If too much information is included, participants might
become identifiable based on their unique combination
of administrative data. We dichotomized age and service
Murdoch et al. BMC Medical Research Methodology 2014, 14:90 Page 9 of 11
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branch in the present study for this reason. Pre-merged
questionnaires also cannot capitalize on new information.
Health care visits occurring after a survey is mailed cannot
be linked into a dataset, for example. Nonetheless, the tech-
nique offers an advance over usual anonymous methods,
particularly in its ability to assess for non-response bias,
and it could easily be applied to other sensitive topics.
This studys strengths include its randomized, controlled
design and demonstration of a unique technique to over-
come what has historically been an important limitation of
anonymous methods namely, an inability to evaluate non-
response bias. We also compared two tracking methods
that can be used in anonymous surveys. Limitations include
its relatively small and unique sample. Since we did not
have access to verifying information, we cannot say how
honestly participants reported their experiences. Findings
generalizability to other sensitive topics, to non-veterans, or
to women is also uncertain. The study was powered to
examine main effects of incentives on response rates, and
we may have made Type II errors when examining second-
ary outcomes, effects of the different tracking/privacy con-
ditions, and potential interactions. When findings appeared
suggestive, however, we described them in the text. We
also made multiple comparisons, which may have inflated
our Type I error.
Conclusion
We anticipated that greater privacy and larger incentives
would be associated with higher response rate, better par-
ticipant representativeness, more survey completeness, and
greater disclosure of potentially sensitive information. Re-
sults showed no association between privacy and response
rate or survey completeness, supported the association be-
tween greater privacy and participant representativeness,
andyieldedmixedeffectsforthedisclosureofsensitivein-
formation. A larger incentive was associated with higher
response rate and better participant representativeness but
no association with survey completeness. In the intermedi-
ate privacy arm, lower incentivenot higherwas associ-
ated with reporting more PTSD symptoms. Otherwise, we
found no statistically significant associations between in-
centive and disclosing potentially sensitive information.
Having shown that different tracking/privacy conditions
yielded different estimates of sensitive information, we can-
not, unfortunately, tell which estimate was most accurate.
Traditionally, higher disclosure rates of sensitive or stigma-
tizing information have been interpreted as being more
accurate than lower rates, but our data suggest that appar-
ently different disclosure rates may simply be a function of
the subpopulations successfully recruited into a survey.
This possibility needs greater investigation. Pre-merged
questionnaires bypassed many of the limitations historic-
ally associated with anonymous survey methods and could
be used to explore non-response issues in future research.
Abbreviations
ID: Identification number; PTSD: Posttraumatic stress disorder; TWEAK: An
acronym of 5 items used to assess problem drinking: T = tolerance, W =
Worried, E = Eye-opener, A = Amnesia, K = Cut down; VA: Department of
Veterans Affairs.
Competing interests
The authors declare they have no competing interests.
Authorscontributions
MM obtained funding; designed the study; oversaw data collection, analysis,
interpretation; and drafted the manuscript. MAP also assisted in obtaining
funding. MAP, AKB, ABS, SN, and JPG contributed to data collection, analysis,
and interpretation of data. MRP contributed to analysis and interpretation of
data. MAP, AKB, ABS, SN, JPG, MRP read and approved the final manuscript.
Authorsinformation
MM, MAP, and MRP are core-investigators; AKB is data manager; and SN is
core statistician for the Center for Chronic Disease Outcomes Research at the
Minneapolis VA Medical Center. ABS is a former Center for Chronic Disease
Outcomes Research data manager and currently works in the Health Economics
Program, Minnesota Department of Health, St. Paul, MN. JPG is a former Center
for Chronic Disease Outcomes Research statistician.
Acknowledgements
The Center for Chronic Disease Outcomes Research is a VA Health Services
Research and Development (HSR&D) Service Center of Excellence (Center
grant #HFP 98-001). This study was supported by grant #GWI 04-352 from VA
HSR&D service. The funding agency had no role in the design, data collection,
analysis, data interpretation, manuscript writing, or decision to submit the
manuscript.
Disclaimer
The views presented in this paper are those of the authors and do not
necessarily represent the views of the Department of Veterans Affairs.
Author details
1
Section of General Internal Medicine, Minneapolis VA Medical Center,
Minneapolis, MN, USA.
2
Center for Chronic Disease Outcomes Research,
Minneapolis VA Medical, One Veterans Drive, Minneapolis, MN 55417, USA.
3
Department of Internal Medicine, University of Minnesota School of
Medicine, Minneapolis, MN, USA.
4
Departments of Psychiatry and Psychology,
Minneapolis VA Medical Center, Minneapolis, MN, USA.
5
Department of
Psychiatry, University of Minnesota School of Medicine, Minneapolis, MN,
USA.
Received: 3 March 2014 Accepted: 7 July 2014
Published: 16 July 2014
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Cite this article as: Murdoch et al.:Impact of different privacy conditions
and incentives on survey response rate, participant representativeness,
and disclosure of sensitive information: a randomized controlled trial.
BMC Medical Research Methodology 2014 14:90.
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The inclusion of Children and Young People (CYP) with Social, Emotional and Mental Health (SEMH) difficulties has proven to be an ongoing challenge for teachers and schools in the UK; teachers view CYP with SEMH-type needs as the most challenging area of Special Educational Need (SEN) to include in mainstream classes (De Boer et al., 2011; DfE, 2019b; Dimitrelllou, 2017) and schools disproportionately exclude CYP with SEMH-type needs compared to other areas of SEN or no SEN at all (Bryant et al., 2018; DfE, 2019b; Graham et al., 2019; Monsen et al., 2014). Despite the government’s commitment to supporting the prevention and effective management of young people’s mental health needs (DoH and DfE, 2017; DfE, 2018; DfE, 2019a), SEMH difficulties are highly prevalent and are expected to increase as a result of the disruption caused by the Covid-19 pandemic (Lee, 2020), placing even greater focus on schools to promote the successful inclusion of students with these needs. Research has consistently highlighted the importance of teacher attitudes and teacher self-efficacy (TSE) in influencing inclusive practices towards CYP with SEN (Amaral et al., 2013; Borg et al., 2011; MacFarlane & Woolfson, 2013; Malak et al., 2018; Pit-ten Cate et al., 2019; Sharma & Sokal, 2016). However, a systematic literature review conducted for this study highlighted that there is currently a lack of research into understanding the relationship between secondary teacher attitudes and efficacy and their behavioural intentions towards the inclusion of CYP, in particular those with SEMH-type needs. Additionally, whilst there is significant evidence into the role of TSE towards inclusive teacher behaviours, there is currently a lack of research into the role of teacher collective efficacy (CTE) in determining inclusive practices. This study adopted the Theory of Planned Behaviour (Ajzen, 1991) to investigate the relationship between teacher attitudes (both beliefs and feelings), TSE (perceived behavioural control), CTE (subjective norm) and behavioural intentions towards the inclusion of CYP with SEMH needs. Adopting a cross-sectional survey design, secondary school teachers (n=101) from mainstream schools participated in an online questionnaire. The results of the study found that strength of secondary teacher self-efficacy was significantly higher for teachers with over fifteen years of experience compared to those with less than five years of experience. Only teacher attitudes (both beliefs and feelings) were individually found to be a predictor of behavioural intentions towards the inclusion of CYP with SEMH needs. The implications of the findings for both research and professional practice are explored including; how headteachers can strengthen teacher attitudes towards inclusion to enable inclusive practices and how educational psychologists may support a deeper understanding of SEMH through specialist training and groupbased problem-solving supervision.
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Caring for the elderly is a requirement for development. Ghana’s unpreparedness to meet the nutritional need of the steadily growing elderly population made this study delve into the food habits of the elderly. This study focused on the physiological status and food habits of the elderly in the Kwahu- South District of Ghana using the sequential explanatory mixed-method design. The study first exposes the reader to theoretical and empirical surveys pertinent to the topic from a global perspective focusing on Ghana. With the aid of a questionnaire and a focus group discussion guide, the researchers solicited data from 103 respondents, 97 for the quantitative and 6 for the qualitative phase, respectively, who were sampled using simple random sampling and purposive sampling techniques. Data collected were analysed using frequency counts and percentages with version 20 of the SPSS for the quantitative aspect, whereas emerging themes were used for the qualitative data. Findings of this study established that difficulty in chewing a\nd swallowing, immobility, gastrointestinal challenges and diminished sensory abilities such as reduced taste and poor eyesight were identified as the physiological characteristics of the elderly. Food taste, texture, and smell are the major organoleptic factors influencing the food choice of the elderly in the study area. Again, psycho-socioeconomic factors like emotions elicited on seeing given foods, perceptions one develops seeing one eating particular foods, cost, and availability of foods emerged as broad determinants of adults’ food habits in this study. The study also found out that foods such as game, fish, egg, plantain, potatoes, fruits, and vegetables ranked high on the list of likes of the elderly over the study period. This study, therefore, recommends that dieticians formulate a standardised dietary plan that considers the physiological characteristics of the elderly to enjoy their meals.
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This paper is an introduction to the literature on the sexual assault of adult males. Various myths concerning the survivors, perpetrators and plausibility of such assaults are challenged. Problems relating to official statistics on the prevalence of such assaults are briefly discussed. Prevalence data from a community sample and a study of gay men are presented. There currently exists little empirical research on the psychological sequelae of sexual assaults on men. However, data from case studies of men assaulted by men or women have found that survivors may exhibit a number of symptoms, including anxiety, depression, post-traumatic stress disorder, and sexual problems including confusion about sexual orientation. Evidence concerning optimal treatment strategies for survivors is not available. However, a number of points relating to the early and delayed management of survivors are suggested.
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In a survey about euthanasia, 1,600 critical care nurses were randomly assigned to receive either three complete, anonymous mailings of the questionnaire or, with each mailing, a coded postcard to be returned separately from the questionnaire to reduce subsequent mailings to previous responders. The response rate in these two groups was 76.5% [95% confidence interval (CI) = 73.6-79.4%] and 69% (95% CI = 65.7-72.4%), respectively. The two strategies yielded similar responses, and costs were much lower for the postcard group. Using coded postcards to be returned separately from completed instruments appears to lower the response rate to anonymous mail surveys, but it also lowers cost and may not introduce additional bias. Language: en
Article
Postal and electronic questionnaires are widely used for data collection in epidemiological studies but non-response reduces the effective sample size and can introduce bias. Finding ways to increase response to postal and electronic questionnaires would improve the quality of health research. OBJECTIVES: To identify effective strategies to increase response to postal and electronic questionnaires. SEARCH STRATEGY: We searched 14 electronic databases to February 2008 and manually searched the reference lists of relevant trials and reviews, and all issues of two journals. We contacted the authors of all trials or reviews to ask about unpublished trials. Where necessary, we also contacted authors to confirm methods of allocation used and to clarify results presented. We assessed the eligibility of each trial using pre-defined criteria. SELECTION CRITERIA: Randomised controlled trials of methods to increase response to postal or electronic questionnaires. DATA COLLECTION AND ANALYSIS: We extracted data on the trial participants, the intervention, the number randomised to intervention and comparison groups and allocation concealment. For each strategy, we estimated pooled odds ratios (OR) and 95% confidence intervals (CI) in a random-effects model. We assessed evidence for selection bias using Egger's weighted regression method and Begg's rank correlation test and funnel plot. We assessed heterogeneity among trial odds ratios using a Chi(2) test and the degree of inconsistency between trial results was quantified using the I(2) statistic. MAIN RESULTS: PostalWe found 481 eligible trials. The trials evaluated 110 different ways of increasing response to postal questionnaires. We found substantial heterogeneity among trial results in half of the strategies. The odds of response were at least doubled using monetary incentives (odds ratio 1.87; 95% CI 1.73 to 2.04; heterogeneity P < 0.00001, I(2) = 84%), recorded delivery (1.76; 95% CI 1.43 to 2.18; P = 0.0001, I(2) = 71%), a teaser on the envelope - e.g. a comment suggesting to participants that they may benefit if they open it (3.08; 95% CI 1.27 to 7.44) and a more interesting questionnaire topic (2.00; 95% CI 1.32 to 3.04; P = 0.06, I(2) = 80%). The odds of response were substantially higher with pre-notification (1.45; 95% CI 1.29 to 1.63; P < 0.00001, I(2) = 89%), follow-up contact (1.35; 95% CI 1.18 to 1.55; P < 0.00001, I(2) = 76%), unconditional incentives (1.61; 1.36 to 1.89; P < 0.00001, I(2) = 88%), shorter questionnaires (1.64; 95% CI 1.43 to 1.87; P < 0.00001, I(2) = 91%), providing a second copy of the questionnaire at follow up (1.46; 95% CI 1.13 to 1.90; P < 0.00001, I(2) = 82%), mentioning an obligation to respond (1.61; 95% CI 1.16 to 2.22; P = 0.98, I(2) = 0%) and university sponsorship (1.32; 95% CI 1.13 to 1.54; P < 0.00001, I(2) = 83%). The odds of response were also increased with non-monetary incentives (1.15; 95% CI 1.08 to 1.22; P < 0.00001, I(2) = 79%), personalised questionnaires (1.14; 95% CI 1.07 to 1.22; P < 0.00001, I(2) = 63%), use of hand-written addresses (1.25; 95% CI 1.08 to 1.45; P = 0.32, I(2) = 14%), use of stamped return envelopes as opposed to franked return envelopes (1.24; 95% CI 1.14 to 1.35; P < 0.00001, I(2) = 69%), an assurance of confidentiality (1.33; 95% CI 1.24 to 1.42) and first class outward mailing (1.11; 95% CI 1.02 to 1.21; P = 0.78, I(2) = 0%). The odds of response were reduced when the questionnaire included questions of a sensitive nature (0.94; 95% CI 0.88 to 1.00; P = 0.51, I(2) = 0%).ElectronicWe found 32 eligible trials. The trials evaluated 27 different ways of increasing response to electronic questionnaires. We found substantial heterogeneity among trial results in half of the strategies. The odds of response were increased by more than a half using non-monetary incentives (1.72; 95% CI 1.09 to 2.72; heterogeneity P < 0.00001, I(2) = 95%), shorter e-questionnaires (1.73; 1.40 to 2.13; P = 0.08, I(2) = 68%), including a statement that others had responded (1.52; 95% CI 1.36 to 1.70), and a more interesting topic (1.85; 95% CI 1.52 to 2.26). The odds of response increased by a third using a lottery with immediate notification of results (1.37; 95% CI 1.13 to 1.65), an offer of survey results (1.36; 95% CI 1.15 to 1.61), and using a white background (1.31; 95% CI 1.10 to 1.56). The odds of response were also increased with personalised e-questionnaires (1.24; 95% CI 1.17 to 1.32; P = 0.07, I(2) = 41%), using a simple header (1.23; 95% CI 1.03 to 1.48), using textual representation of response categories (1.19; 95% CI 1.05 to 1.36), and giving a deadline (1.18; 95% CI 1.03 to 1.34). The odds of response tripled when a picture was included in an e-mail (3.05; 95% CI 1.84 to 5.06; P = 0.27, I(2) = 19%). The odds of response were reduced when "Survey" was mentioned in the e-mail subject line (0.81; 95% CI 0.67 to 0.97; P = 0.33, I(2) = 0%), and when the e-mail included a male signature (0.55; 95% CI 0.38 to 0.80; P = 0.96, I(2) = 0%). AUTHORS' CONCLUSIONS: Health researchers using postal and electronic questionnaires can increase response using the strategies shown to be effective in this systematic review.
Chapter
Postal questionnaires are widely used for data collection in epidemiological studies but non-response reduces the effective sample size and can introduce bias. Finding ways to increase response rates to postal questionnaires would improve the quality of health research. Objectives To identify effective strategies to increase response rates to postal questionnaires. Search strategy We aimed to find all randomised controlled trials of strategies to increase response rates to postal questionnaires. We searched 14 electronic databases to February 2003 and manually searched the reference lists of relevant trials and reviews, and all issues of two journals. We contacted the authors of all trials or reviews to ask about unpublished trials. Where necessary, authors were also contacted to confirm methods of allocation used and to clarify results presented. We assessed the eligibility of each trial using pre-defined criteria. Selection criteria Randomised controlled trials of methods to increase response rates to postal questionnaires. Data collection and analysis We extracted data on the trial participants, the intervention, the number randomised to intervention and comparison groups and allocation concealment. For each strategy, we estimated pooled odds ratios and 95% confidence intervals in a random effects model. Evidence for selection bias was assessed using Egger's weighted regression method and Begg's rank correlation test and funnel plot. Heterogeneity among trial odds ratios was assessed using a chi-square test at a 5% significance level and the degree of inconsistency between trial results was quantified using I-2. Main results We found 372 eligible trials. The trials evaluated 98 different ways of increasing response rates to postal questionnaires and for 62 of these the combined trials included over 1,000 participants. We found substantial heterogeneity among trial results in half of the strategies. The odds of response were at least doubled using monetary incentives (odds ratio 1.99, 95% CI 1.81 to 2.18; heterogeneity p<0.00001, I-2=78%), recorded delivery (2.04, 1.60 to 2.61; p=0.0004, I-2=69%), a teaser on the envelope - e.g. a comment suggesting to participants that they may benefit if they open it (3.08, 1.27 to 7.44) and a more interesting questionnaire topic (2.44, 1.99 to 3.01; p=0.74, I-2=0%). The odds of response were substantially higher with pre-notification (1.50, 1.29 to 1.74; p<0.00001, I-2=90%), follow-up contact (1.44, 1.25 to 1.65; p<0.0001, I-2=68%), unconditional incentives (1.61, 1.27 to 2.04; p<0.00001, I-2=91%), shorter questionnaires (1.73, 1.47 to 2.03; p<0.00001, I-2=93%), providing a second copy of the questionnaire at follow-up (1.51, 1.13 to 2.00; p<0.00001, I-2=83%), mentioning an obligation to respond (1.61, 1.16 to 2.22; p=0.98, I-2=0%) and university sponsorship (1.32, 1.13 to 1.54; p<0.00001, I-2=83%). The odds of response were also increased with non-monetary incentives (1.13, 1.07 to 1.21; p<0.00001, I-2=71%), personalised questionnaires (1.16, 1.07 to 1.26; p<0.00001, I-2=67%), use of coloured as opposed to blue or black ink (1.39, 1.16 to 1.67), use of stamped return envelopes as opposed to franked return envelopes (1.29, 1.18 to 1.42; p<0.00001, I-2=72%), an assurance of confidentiality (1.33, 1.24 to 1.42) and first class outward mailing (1.12, 1.02 to 1.23). The odds of response were reduced when the questionnaire included questions of a sensitive nature (0.94, 0.88 to 1.00; p=0.51, I-2=0%), when questionnaires began with the most general questions (0.80, 0.67 to 0.96), or when participants were offered the opportunity to opt out of the study (0.76, 0.65 to 0.89; P=0.46, I-2=0%). Authors' conclusions Health researchers using postal questionnaires can increase response rates using the strategies shown to be effective in this systematic review.
Article
To estimate frequencies of behaviors not carried out in public view, researchers generally must rely on self-report data. We explored 2 factors expected to influence the decision to reveal: (a) privacy (anonymity vs. confidentiality) and (b) normalization (providing information so that a behavior is reputedly commonplace or rare). We administered a questionnaire to 155 undergraduates. For 79 respondents, we had corroborative information regarding a negative behavior: cheating. The privacy variable had an enormous impact; of those who had cheated, 25% acknowledged having done so under confidentiality, but 74% admitted the behavior under anonymity. Normalization had no effect. There were also dramatic differences between anonymity and confidentiality on some of our other questions, for which we did not have validation.