Impact of informed-choice invitations on diabetes screening knowledge, attitude and intentions: an analogue study

RESEARCH ARTICLE Open Access
Impact of informed-choice invitations on diabetes
screening knowledge, attitude and intentions:
an analogue study
Eleanor Mann1, Ian Kellar2, Stephen Sutton2, Ann Louise Kinmonth2, Matthew Hankins3, Simon Griffin4,
Theresa M Marteau1*
Abstract
Background: Despite concerns that facilitating informed choice would decrease diabetes screening uptake,
‘informed choice’ invitations that increased knowledge did not affect attendance (the DICISION trial). We explored
possible reasons using data from an experimental analogue study undertaken to develop the invitations. We tested
a model of the impact on knowledge, attitude and intentions of a diabetes screening invitation designed to
facilitate informed choices.
Methods: 417 men and women aged 40-69 recruited from town centres in the UK were randomised to receive
either an invitation for diabetes screening designed to facilitate informed choice or a standard type of invitation.
Knowledge of the invitation, attitude towards diabetes screening, and intention to attend for diabetes screening
were assessed two weeks later.
Results: Attitude was a strong predictor of screening intentions (b = .64, p = .001). Knowledge added to the
model but was a weak predictor of intentions (b = .13, p = .005). However, invitation type did not predict attitudes
towards screening but did predict knowledge (b = -.45, p = .001), which mediated a small effect of invitation type
on intention (indirect b = -.06, p = .017).
Conclusions: These findings may explain why information about the benefits and harms of screening did not
reduce diabetes screening attendance in the DICISION trial.
Background
Invitations for screening have traditionally focused on
maximising uptake, providing only information about
population benefits [1]. Recent health policy in the UK
and elsewhere has shifted towards the view that partici-
pation in screening should reflect individual informed
choices, informed about the potential harms as well as
individual benefits of screening [2,3]. In 2009, patients’
right to information and choice about their healthcare
became a legal right [4]. Informed choices can be con-
sidered to have two core characteristics: first, they
should be informed by best current evidence; and sec-
ond, they should reflect the decision-maker’s values
[5,6]. In the case of diabetes, the likelihood of health
benefits for individuals arising from screening is low,
and there have been concerns that telling people about
the limited benefits and possible harms will reduce
screening uptake [1,7]. At a population level this may
increase the burden on the healthcare system as people
with undiagnosed and therefore untreated diabetes have
increased risk of developing complications. These con-
cerns that patient informed choice might reduce screen-
ing uptake may explain why the informed choice policy
is not generally implemented in screening. However, the
veracity of this concern remains unknown [7].
The public health benefits of earlier detection and
treatment of type 2 diabetes as a result of screening are
uncertain [8,9]. The most efficient method of screening
is likely to incorporate a step-wise process targeting
those at highest risk as opposed to inviting everyone
* Correspondence: theresa.marteau@kcl.ac.uk
1Psychology Department (at Guy’s), Health Psychology Section, 5th Floor
Bermondsey Wing, Guy’s Campus, London SE1 9RT, UK
Full list of author information is available at the end of the article
Mann et al. BMC Public Health 2010, 10:768
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© 2010 Mann et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
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directly for a diagnostic test [10]. A step-wise procedure
screens out many of those unlikely to have diabetes, but
results in a high false positive rate at initial testing; most
of the people invited back for further testing will not
have diabetes at that time.
According to the Theory of Planned Behaviour [11],
which has been widely applied to screening participa-
tion, salient beliefs about the personal consequences of
the target behaviour determine attitude toward the
behaviour which in turn influences intention to perform
that behaviour; to the extent that the behaviour is under
volitional control, intention is a proximal determinant of
behaviour. A recent meta-analysis [12] of studies using
the theory of planned behaviour to predict screening
uptake found that attitudes towards screening were a
good predictor of screening intentions (r = .51, p <
.001), and that intentions were a good predictor of
screening uptake (r = .42, p < .001). If an increase in
knowledge leads to changes in salient behavioural beliefs
i.e. those that influence attitudes, then this may lead to
changes in intentions and behaviour. Therefore if giving
information about screening limitations leads to more
negative salient beliefs about screening we would predict
that fewer people would attend for screening.
DICISION is a randomised clinical trial of an
informed choice invitation to diabetes screening. It
aimed to test the validity of concerns that facilitating
informed choices would lead to reduced attendance for
screening, particularly in the more socially deprived. As
part of the DICISION trial, an experimental analogue
study was conducted in order to develop the informed
choice invitation [13]. The invitation contained evi-
dence-based information, in accordance with General
Medical Council (GMC) guidelines [2], and was
designed to be read and understood across a wide range
of literacy. Rates of informed choice were significantly
higher after reading the invitation designed to facilitate
informed choice compared to a standard one, similar to
those currently used. The invitation was then used in a
clinical trial of diabetes screening uptake [14]. In the
main trial no difference in screening uptake was found
between participants who received the informed choice
invitation and those receiving the standard invitation
[15]. Impacts of informed choice on screening uptake
might be expected to vary depending on the condition
screened for. For example, some screening tests can
entail physical harms that include disability, e.g. prostate
cancer [16], whereas the potential harms of diabetes
screening may be considered less harmful, for example,
unnecessary worry as a result of false positive test
results. Mathieu, Barratt, Davey et al [17] found no dif-
ference in breast cancer screening uptake in women
receiving an informed choice decision aid compared to
usual care. Trevena, Irwig and Barratt [18] found no
impacts of a decision aid on rates of self reported use of
colorectal cancer screening kits. By contrast Krist,
Woolf, Johnson and Kearns [19] found fewer requests
for prostate cancer screening tests following a decision
aid. In the DICISION trial, to avoid possible measure-
ment effects, questionnaire data were not collected until
after the primary outcome (attendance) had been mea-
sured. However, data from the experimental analogue
study can be used to model the impact of an invitation
designed to foster choice on the cognitive antecedents
of screening intentions and thus to explore possible
explanations for the findings of the DICISION trial.
The present study
The present study reports data from the experimental
analogue study conducted prior to the DICISION trial.
Intentions to attend for screening are used as the pri-
mary outcome. Although screening intentions do not
equate to actual attendance, they are a good predictor
[12]. The analogue design also ensures that all partici-
pants view the invitation, which could not be controlled
for in the clinical trial, so this study tests whether the
materials used in the DICISION trial manipulate cogni-
tions as hypothesised and serves as an explanatory
account of the objective outcomes of the DICISION
trial. The impact on rates of informed choice of the
invitation developed for the trial, and cognitive differ-
ences by invitation type were reported by Kellar et al
[13]. The present study tests whether invitation type
impacts on intention, mediated by attitude, as would be
predicted by the theory of planned behaviour.
Objective
To test a model of the impact on knowledge, attitude
and intentions of a diabetes screening invitation
designed to facilitate informed choices.
Methods
Participants
Members of the public were approached by market
research representatives in the street, in town centres
around the UK between February and April 2006. Eligi-
ble participants were aged between 40 and 69 years,
with no previous diagnosis of diabetes, who agreed to
provide demographic details and accept a follow-up visit
at their homes 2 weeks later. Additionally, a quota was
set of 50% of participants having finished full-time edu-
cation at 16 or before. All questionnaire measures were
delivered verbally. 196 males and 221 females took part.
They were told that they were at a higher risk of devel-
oping type 2 diabetes because they were 40 years old or
over. Participants then viewed one invitation taken from
the top of a randomly ordered pile (either standard or
one of two versions of an informed choice invitation).
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The materials were ordered in a way that the invitation
type was hidden until the recruitment process was com-
pleted. Moreover, interviewers were not aware of the
direction of anticipated effect of materials, and materials
were dummy-coded, so that no sense of intervention or
control would have been communicated to interviewers
or participants. After the participant had read the invita-
tion they were told:
“[it is] an invitation to attend a diabetes screening
appointment. The appointment will not take place,
but please vividly imagine that you have received
this from your GP regarding a real appointment“.
Two weeks later the participants completed a verbally-
administered questionnaire without referring back to the
invitation, conducted at participants’ homes by a market
researcher. Participants received £5 on completion of
the study.
The research was conducted in compliance with the
Helsinki Declaration [20] and ethical approval was
obtained from Cambridge University Ethics Committee.
Intervention materials
Two invitations to attend for diabetes screening were
developed for this study: a standard invitation (control
group), and an invitation designed to facilitate informed
choice (see additional files 1 and 2). Two versions of the
informed choice invitation were developed. In the first,
participants were asked to list “good things” and “bad
things” about screening for diabetes. In the second, par-
ticipants were asked to list “good feelings” and “bad feel-
ings”. There were no significant effects of this
manipulation and the two groups were treated as a sin-
gle group in the analysis reported here.
Standard invitation
The standard invitation, shown in additional file 1, was
based upon invitations commonly used to invite people
for diabetes and coronary heart disease screening [21]. It
presented a brief didactic argument, describing only
benefits of attending for screening. It explained that the
participant might have a higher chance of developing
type 2 diabetes, and that diabetes has serious long term
consequences.
Informed choice invitation
The informed choice invitation, shown in additional file
2, contained the information described above, plus
information which included the limited benefits and
potential harms of attending for screening. The text of
the invitation explained both absolute risks and relative
risk using frequencies, e.g. “If 100 people had the test,
about 63 would get this result”. Previous studies have
shown that risk information is most readily understood
using frequencies in this way [22]. Participants were
encouraged to make a choice that reflected their values
by prompting them to evaluate the consequences and
asking them to record their decision to attend or not.
Providing information about diabetes risk and
consequences of screening
This section was developed from the UK General Medi-
cal Council (GMC) guidelines for providing sufficient
information when gaining patient consent [2]. These
guidelines include purpose of screening, details of diag-
nosis and prognosis with and without treatment, prob-
ability of benefits and risks, and emphasis on patient
choice. The invitation began with an emphasis on
patient choice “Screening for diabetes. It’s your decision“,
and a statement that the participant was being offered
screening for type 2 diabetes because they might have a
higher chance of developing the condition. An explana-
tion of diabetes and the screening procedure followed,
then an explanation of the expected results and what
they mean for the patient. Finally, the benefits and
harms of attending for screening were outlined, includ-
ing likely prognosis of early treatment compared to
standard treatment following clinical diagnosis and the
potential for unnecessary worry following false positive
results.
Encouraging participants to make a choice
At the end of the hypothetical invitation letter, partici-
pants were asked to consider the consequences of their
attending diabetes screening and to indicate their deci-
sion as to whether to go for screening or not, or to
think more about the decision.
The content and format of the informed choice invita-
tion were refined through extensive piloting using “think
aloud” techniques. Both invitations were designed to be
comprehensible to those with a reading age of 11 or
above (Flesch Reading Ease score was 71.52 and 72.88
for the standard and the informed choice invitations,
respectively). Rates of informed choice were significantly
higher after reading the informed choice invitation com-
pared to the standard invitation [13].
Measures
Gender, age group (40-49, 50-59, 60-69 years), and job
title of the highest earner in the household were recorded.
Job title was used to assign a social grade [23]: Grades A
and B encompassed mid or top level management and
other high level professionals, grade C1 included junior
management and other non manual occupations, grade
C2 included skilled manual workers, grade D included
semi and unskilled workers, and grade E referred to the
state dependent and those without regular employment.
Strength of intention to attend for screening (herein
termed ‘intention’) was measured as a behavioural
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expectation using two items: “Would you have the dia-
betes screening test?” (5 point scale; 1 - definitely no, 2
- probably no, 3 - not sure, 4 - probably yes; 5 - defi-
nitely yes), and “How likely is it that you would have
the diabetes screening test?” (7 point scale from 1 -
extremely unlikely to 7 - extremely likely). An strength
of intention scale with a zero mid point was constructed
by subtracting four from responses to the 7-point scale
(-3 to 3) and three from the 5-point scale (-2 to 2). The
5-point scale was converted to a scale equivalent to the
7-point scale by multiplying the values by 7/5 (-2.8 to
2.8). Subsequently individuals’ scores for the two scales
(r = .76, p < .001) were summed resulting in a scale ran-
ging from -5.8 to 5.8.
Attitude was indexed by the mean of six items
adapted from Marteau et al [6] measured on 7-point
scales: “For me, having the screening test for diabetes
would be...” (not worthwhile - worthwhile; unimportant
- important; harmful - not harmful; not beneficial-bene-
ficial; not a good thing - a good thing; a bad thing - not
a bad thing) (Cronbach’s a = .88). Higher attitude scores
indicate more positive attitude (range: 1 to 7)
Eight multiple choice items measured participants’
knowledge of the implications of diabetes screening.
These items were developed for this study based on
GMC guidelines for providing information about screen-
ing [2]. Examples included “What are the possible harms
of screening for diabetes?”, “How effective is early treat-
ment for diabetes in preventing long term problems?”,
and “For most people, what is the most likely test result
from diabetes screening?” (see additional file 3). Higher
knowledge scores indicate better knowledge (Range 1 to
8).
Analysis
T tests are used to describe the impacts of the informed
choice invitation on knowledge, attitudes and intentions.
Pearson’s correlations are used to explore the associa-
tions between knowledge, attitudes and intentions. 400
participants are needed for 80% power to detect a small
effect (d = .3) of the informed choice invitation on
knowledge, attitudes and intentions (assuming an alpha
of .05 and a two-sided test).
The impact of the invitations on strength of intentions
was modelled using AMOS 7. A path model was speci-
fied in which invitation type influenced knowledge,
which influenced attitude, which in turn influenced
intention. No other paths were specified. A maximum
likelihood bootstrapping procedure (2000 samples) was
used to estimate the model. Model fit was tested with
the chi square test (c2), root mean square error of
approximation (RMSEA), the comparative fit index
(CFI), and the standardized root mean square residual
(SMSR). Good fit is indicated when c2 is non-significant
(although this is rare in samples over 100), RMSEA is
less than .05 (although close fit for RMSEA is <.08 [24]),
CFI is greater than .95 and SMSR is less than .08 [25].
In addition, a multiple group analysis was conducted to
test whether the model relating knowledge, attitude and
strength of intention differed in the two invitation
groups. This was done by constraining the regression
coefficients to be the same in the two groups and exam-
ining the reduction in fit compared with a model in
which these parameters were freely estimated in each of
the two groups.
Results
Participants’ demographic characteristics are sum-
marised in Table 1. The modal age group was 40-49
and 53% (221) were female. The modal social grade was
C1 (supervisory or clerical, junior managerial, adminis-
trative or professional), reflecting national data, but
overall this sample had a higher proportion of less
deprived participants than that found in the UK popula-
tion [26].
139 participants viewed the standard invitation to
attend for diabetes screening and 278 participants
viewed one of the invitations designed to facilitate
informed choice. Five participants from the standard
group and five participants from the informed choice
group did not complete follow up measures two weeks
later, resulting in 134 in the standard group and 273 in
the informed choice group (n = 407, 98% response rate).
There were no differences in age between the standard
and the informed choice group (c2 (1) = 2.47, p = .29),
sex (c2 (1) = .76, p = .39) or social grade (c2 (1) = 2.65,
p = .11).
Table 1 Demographic characteristics of the study groups
(n = 417).
Invitation Type
Informed choice; n = 278 N
(%)
Standard; n = 139 n
(%)
Age range
40-49 140 (50.4) 66 (47.5)
50-59 90 (32.4) 40 (28.8)
60-69 48 (17.3) 33 (23.7)
Gender
Female 152 (54.7) 69 (49.6)
Male 126 (45.3) 70 (50.4)
Social
Grade
A or B 91 (32.7) 35 (25.2)
C1 104 (37.4) 52 (37.4)
C2 59 (21.2) 29 (20.9)
D 19 (6.8) 20 (14.4)
E 5 (1.8) 3 (2.2)
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Means and standard deviations for knowledge, attitudes
and intentions in the two invitation groups are shown in
Table 2. Those who received the informed choice invita-
tion showed greater knowledge of the potential benefits
and harms of screening than those who received the
standard invitation (difference in means = 1.61 (95%CI:
1.29 to 1.92), p < .001), whereas attitude did not differ
significantly (difference in means = .11 (95%CI: -.08 to
.30), p = .27). Intentions to attend for screening were
slightly stronger in the informed choice group, but the
difference did not reach significance (difference in means
= .49 (95%CI: -.03 to 1.01), p = .07). Rates of informed
choice and group differences in knowledge and attitudes
were originally reported in Kellar et al [13].
Correlations between knowledge, attitudes and inten-
tions are shown in Table 3. Knowledge and attitude
were uncorrelated (r = .01, p = .88), whereas there was
a small positive correlation between knowledge and
intention (r = .13, p = .008). As expected, there was a
large correlation between attitude and intention (r = .64,
p < .001). Correlations did not vary much by invitation
type; there was a significant correlation between knowl-
edge and intention in the informed choice group (r =
.15, p = .01) but not in the standard group (r = .01, p =
.94). However, the difference in correlation size was not
significant (z of difference = 1.33, p = .18).
A model of screening intentions was specified in
which invitation type predicted knowledge, which pre-
dicted attitudes, which predicted strength of intentions.
Fit could be considered adequate: although chi square
was significant (c2(3) = 12.68, p = .005) this is likely to
reflect the large sample size rather than poor fit;
RMSEA was greater than.08 (RMSEA = .09), but CFI
was greater than .95 and SMSR was less than.08 (CFI =
.97; SMSR = .05). The path from knowledge to attitude
was non-significant (b = .01, p = .88), and modification
indices suggested a direct path from knowledge to
intention. This path was added, and the resulting model
(shown in figure 1) was an excellent fit to the data (c2
(2) = 1.35, p = .51; CFI = 1.00; RMSEA = .00; SMSR =
.02). Modification indices did not indicate that the
model could be improved by adding further paths (i.e. a
direct path from invitation to attitude or intention).
Invitation type was a good predictor of knowledge (b =
-.45, p = .001), but did not impact upon attitude either
directly (as indicated by model fit and modification
indices) or indirectly mediated by knowledge (indirect
effects: b = .003 (90%CI -.04 to .03), p = .853). 43% of
the variance in intention was mainly explained by atti-
tudes (b = .64, (90%CI: .58 to .70), p = .001), but knowl-
edge also had a small direct impact on intention (b =
.13 (90%CI: .05 to .20), p = .005), which was unmediated
by attitudes. The indirect effect of the invitation on
intention, mediated by knowledge, was small but signifi-
cant (indirect b = -.06 (90%CI: -.10 to -.02), p = .017).
The direct effect of knowledge on intention appeared to
be driven by the informed choice invitation, as there
was no correlation between knowledge and intention in
the standard group (r = .01, p = .94). A multiple group
analysis was then conducted, comparing the model (fig-
ure 1) separately for the two groups. These showed no
significant reduction in fit when the regression coeffi-
cients for attitude and knowledge were constrained to
be the same in the two invitation groups (c2(2) = 4.83,
p = .09), suggesting that the same model was applicable
to the standard group as to the informed choice group.
Discussion
These results suggest that informed choice invitations
that increase knowledge alone have little effect on atti-
tudes or strength of intentions to attend for screening.
Attitudes and intentions to attend for screening were
Table 2 Knowledge, attitudes and intentions (mean
(SDs)) overall and in each invitation group.
Overall
(n = 407)
Informed choice
(n = 273)
Standard
(n = 134)
Knowledge 4.97 (1.69) 5.49 (1.53) 3.89 (1.47)
Attitude 6.21 (.92) 6.25 (.89) 6.14 (.98)
Intention 4.01 (2.38) 4.17 (2.22) 3.68 (2.65)
Higher knowledge scores indicate better knowledge of screening (range: 1 to
8); Higher attitude scores indicate more positive attitudes towards attending
for screening (range 1 to 7); higher intention scores indicate stronger
intentions to attend for screening (-5.8 to + 5.8)
Table 3 Correlations (Pearson’s r) between knowledge,
attitudes and intentions overall and by group.
Overall
(n = 407)
Informed choice
(n = 273)
Standard
(n = 134)
Knowledge-Attitude .01 .00 -.06
Knowledge-Intention .13** .15* .01
Attitude-Intention .64*** .61*** .70***
* p < .05; ** p < .01; *** p < .001
R2 =.20
KnowledgeInvitation Attitude
R2 = .43
Intention
.64***
E1 E2 E3
-.45***
.13** (.05 to .20)
.01
R2 =.00
(-.07 to .10) (-.51 to -.38) (.58 to .70)
Figure 1 Model of the impact of the informed choice invitation
on screening intentions 2 weeks later (n = 407). Notes:
*** p = .001, ** p = .005. Model fit: c2(2) = 1.35, p = .51; CFI = 1.00;
RMSEA = .00, SMSR = .02. 90% confidence intervals for standardised
regression weights shown in brackets Negative b weights between
invitation and knowledge indicate that the informed choice
invitation was associated with higher knowledge. Indirect effect of
invitation on intention = -.06 (90%CI: -.10 to -.02), p = .017. Indirect
effects of invitation on attitude = .003 (90%CI: -.04 to .03), p = .853
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strong regardless of invitation type. Invitation type had a
small indirect effect on intention, mediated by knowl-
edge, but attitudes towards screening were the main
predictor of intention, and were unaffected by invitation
type.
These results suggest that the informed choice invita-
tion did not reduce strength of screening intentions
because it did not result in more negative attitudes
towards screening. Attitudes were the main predictor of
screening intentions, mirroring findings in a recent
meta-analysis [12]. However, from the standpoint of the
Theory of Planned Behaviour, an increase in knowledge
would not necessarily be expected to produce a change
in salient beliefs, partly because the recipient might not
apply the information to their own specific case e.g.
“knowing” that many people do not benefit from screen-
ing does not mean that I think I will not benefit from
screening. Even if an increase in knowledge does pro-
duce changes in salient beliefs, these changes may not
all be in the same direction i.e. an increase in knowledge
could produce an increase or a decrease in attitude. Our
findings are generally consistent with those of previous
studies. A review by Fox [27] found few studies of
informed choice materials in which changing knowledge
resulted in changes in attitudes. Of nine trials of written
information, eight assessed knowledge and four assessed
attitudes. While five out of eight trials assessing knowl-
edge showed increased knowledge, only one of those
assessing attitudes showed any change in attitude
(towards more negative screening attitudes [28]). Con-
cerns that facilitating informed choice will reduce
screening uptake seem to be based upon the unfounded
assumption that providing information changes beha-
viour. At best, information-based interventions have
shown mixed effects on behaviour [27,29,30]. We did
find a small indirect effect of the informed choice invita-
tion on intention, mediated by a positive effect of
knowledge. It was not, however, large enough to trans-
late into significant invitation group differences. Either
the effect was a chance finding or it was a robust effect
too small to be of applied value.
Using the same invitations, the DICISION trial found
no differences in attendance for screening. Thus the
present study adds to the growing body of evidence that
providing information designed to facilitate informed
choice is unlikely to have significant detrimental impacts
upon behaviour. However, whilst the invitation may
have increased knowledge sufficiently, it may have failed
to facilitate choice. The present study reported positive
attitudes and strong intentions to attend for screening.
By contrast, in the DICISION trial, uptake of screening
was lower, particularly in those with high levels of social
deprivation. This suggests that screening attendance
may have been driven more by practical barriers than by
cognitive differences. Such findings would indicate that
participants did not accurately envisage the practical bar-
riers they would face if actually invited for screening,
rather than reflecting low motivation to attend. Saidi,
Sutton and Bickler [31] found practical barriers were the
most commonly reported reason for non-attendance in
the unemployed. Most interventions designed to facilitate
informed choices concentrate on increasing knowledge
only. Future interventions need to consider how best to
enable people to act in accordance with their intentions.
The potential benefits and harms of screening vary
widely depending on condition screened for, which may
influence the impacts of informed choice. As a result
the generalisability of the findings to screening for other
conditions is unknown. The harms that can arise from
screening for diabetes are generally not considered ser-
ious [32,33] and were described in the invitations we
used as comprising worry prior to an appointment and
false reassurance following a “screen negative” test
result. In contrast, undergoing other screening tests can
entail physical harms that include disability and even
death e.g. colonoscopy [34]. Evidence of the impact of
knowledge about such potential harms and the uncer-
tain limited individual benefit of screening is mixed
[27,30]. It is important to study screening for different
conditions, in order to find out whether it is valid to
talk about the impacts of informed choice on screening
uptake in general, or whether we should treat screening
tests for different conditions separately.
If making informed choices does not change decisions
at all, is there a benefit of investing resources in facili-
tating informed choice? Informed choice might not
change decisions, but instead increase well-being or
have other beneficial effects. Evidence suggests that bet-
ter knowledge of screening reduces anxiety in those
recalled for further testing [35]; although diabetes
screening does not seem to cause high levels of anxiety
[32]. More research into the cost-effectiveness of facili-
tating informed choice may be needed, but setting the
threshold at which the costs of facilitating informed
choice outweigh the benefits is a value judgement.
There are several limitations to this study. Although
the present sample was at risk of diabetes because they
were over 40, they were not necessarily representative of
the highest risk individuals in this age group. Only peo-
ple who visited town centres during normal office hours
and would accept a home visit for follow up were
included, and £5 incentive may have also added a selec-
tion bias. The lack of anonymity with verbally delivered
questionnaires might encourage socially desirable
responding, but use of neutral market researchers may
reduce this effect, compared to, for example, a member
of the study research team. The drawbacks of an analo-
gue design must be acknowledged. We make the
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assumption that intentions obtained through imagining
a hypothetical screening scenario are a good indication
of actual attendance for screening. Although intentions
are the best predictor of screening uptake overall [12],
intentions to attend for screening were higher than
actual uptake found in the clinical context of the main
DICISION trial. Furthermore, we suggest an explanatory
account of the DICISION trial findings because we test
the same intervention materials, but the two studies are
independent, using separate samples of participants, and
therefore our conclusions are tentative pending verifica-
tion in a clinical population. Finally, our conclusions are
generalisable only to diabetes screening until further
research indicates to what extent impacts of informed
choice in screening are dependent upon the context.
Conclusions
An invitation designed to facilitate informed choice that
increased knowledge alone did not affect intentions,
because it did not affect attitudes, the main predictor of
intentions. Attitudes and intentions to attend for screen-
ing were strong regardless of information received.
These findings add to a growing body of evidence show-
ing that providing information about the potential bene-
fits and harms of attending for screening will not reduce
screening uptake and therefore does not conflict with
maximising population health. However, facilitating
informed choice may require interventions that bridge
the intention-action gap in screening uptake, particularly
among socially deprived groups.
Additional material
Additional file 1: The standard invitation. The invitation received by
participants in the control arm
Additional file 2: The informed choice invitation. The invitation
received by participants in the intervention arm
Additional file 3: Multiple-choice diabetes screening knowledge
questionnaire. The 8 items that comprise the multiple-choice diabetes
screening knowledge questionnaire
Acknowledgements
We thank study participants and the staff at Bretton Medical Practice,
Peterborough; Old Fletton Surgery, Peterborough; The Rookery Medical
Centre, Newmarket; and Thorney Medical Practice, Peterborough; the nurses
who conducted the screening clinics led by Marian Bosman; MRC Field
Epidemiology team; Nicola Popplewell, Helen Morris, Kate Williams and
Rachel Crockett for their contribution to the development of the study and
the materials
Author details
1Psychology Department (at Guy’s), Health Psychology Section, 5th Floor
Bermondsey Wing, Guy’s Campus, London SE1 9RT, UK. 2Department of
Public Health and Primary Care, University of Cambridge, Forvie Site,
Robinson Way, Cambridge, CB2 0SR, UK. 3Division of Primary Care and Public
Health and Institute of Postgraduate Medicine, Brighton and Sussex Medical
School, Falmer, BN1 9PH, UK. 4MRC Epidemiology Unit, Institute of Metabolic
Science, Box 285, Addenbrooke’s Hospital, Hills Road, Cambridge, CB2 0QQ,
UK.
Authors’ contributions
EM conducted statistical analysis and drafted the manuscript; IK is the study
coordinator; MH provided statistical analysis support; TMM, ALK, SG and SS
are Principal Investigators; TMM is the paper guarantor. All authors read and
approved the final manuscript.
Competing interests
The authors declare that they have no competing interests.
Received: 6 July 2010 Accepted: 17 December 2010
Published: 17 December 2010
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Cite this article as: Mann et al.: Impact of informed-choice invitations
on diabetes screening knowledge, attitude and intentions: an analogue
study. BMC Public Health 2010 10:768.
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