British Journal of Clinical Psychology (2017)
©2017 The British Psychological Society
Acceptance and commitment therapy (ACT) for
clinically distressed health care workers:
Waitlist-controlled evaluation of an ACT
workshop in a routine practice setting
Cerith S. Waters
* , Neil Frude
, Paul E. Flaxman
School of Psychology, Cardiff University, Wales, UK
Psychology and Counselling, Whitchurch Hospital, Cardiff University, Wales, UK
Department of Psychology, City University London, UK
Objectives. To examine the effects of a 1-day acceptance and commitment therapy
(ACT) workshop on the mental health of clinically distressed health care employees, and
to explore ACT’s processes of change in a routine practice setting.
Design. A quasi-controlled design, with participants block allocated to an ACT
intervention or waiting list control group based on self-referral date.
Methods. Participants were 35 health care workers who had self-referred for the ACT
workshop via a clinical support service for staff. Measures were completed by ACT and
control group participants at pre-intervention and 3 months post-intervention. Partic-
ipants allocated to the waitlist condition went on to receive the ACT intervention and
were also assessed 3 months later.
Results. At 3 months post-intervention, participants in the ACT group reported a
signiﬁcantly lower level of psychological distress compared to the control group
(d=1.41). Across the 3-month evaluation period, clinically signiﬁcant change was
exhibited by 50% of ACT participants, compared to 0% in the control group. When
the control group received the same ACT intervention, 69% went on to exhibit
clinically signiﬁcant change. The ACT intervention also resulted in signiﬁcant
improvements in psychological ﬂexibility, defusion, and mindfulness skills, but did
not signiﬁcantly reduce the frequency of negative cognitions. Bootstrapped mediation
analyses indicated that the reduction in distress in the ACT condition was primarily
associated with an increase in mindfulness skills, especially observing and
Conclusions. These ﬁndings provide preliminary support for providing brief ACT
interventions as part of routine clinical support services for distressed workers.
*Corresponding should be addressed to Cerith S. Waters, School of Psychology, Cardiff University, Tower Building, Park Place,
Wales CF10 3AT, UK (email: firstname.lastname@example.org).
A1-day ACT workshop delivered in the context of a routine staff support service was effective for
reducing psychological distress among health care workers.
The brief nature of this group intervention means it may be particularly suitable for staff support and
primary care mental health service settings.
The ﬁndings indicate that the beneﬁcial effects of an ACT workshop on distressed employees’ mental
health were linked to improvements in speciﬁc mindfulness skills.
Study limitations include non-random allocation of participants to the ACT and control groups, and
measurement of mediators and outcome at the same time point (3 months post-intervention).
There has been widespread concern about the individual, organizational, and societal
impact of common mental health difﬁculties among working populations (Hardy, Woods,
& Wall, 2003; Health and Safety Executive (HSE), 2016; Kerr, McHugh, & McCrory, 2009;
Kessler, Merikangas, & Wang, 2008). In the United Kingdom alone, it is estimated that
some 25% of the general working population is experiencing a common mental health
problem at any one time, resulting in approximately 10 million lost working days per
annum (Health and Safety Executive (HSE), 2016; Stride, Wall, & Catley, 2007). Across
different occupations, health care (e.g., nursing) staff have been consistently identiﬁed as
experiencing above average rates of stress, anxiety, and depression (Clegg, 2001; HSE,
2016). However, a surprisingly small proportion of clinically distressed workers are
thought to gain access to evidence-based psychotherapeutic interventions (Hilton et al.,
2008; Seymour & Grove, 2005).
In response to this challenge, there has been long-standing interest in applying
developments in clinical psychology theory and practice to help improve mental health in
workplace settings (e.g., Bunce, 1997; Meichenbaum, 1985; Murphy, 1996; Richardson &
Rothstein, 2008; van der Klink, Blonk, Schene, & van Dijk, 2001). One intervention model
that has been attracting recent interest from occupational health researchers and
practitioners is acceptance and commitment therapy (ACT). Commonly referred to as a
‘contextual’ or mindfulness-based behaviour therapy, ACT places particular emphasis on
the function (rather than the form or frequency) of psychological events –such as
thoughts, feelings, sensations, and behavioural impulses (Hayes, Luoma, Bond, Masuda, &
Lillis, 2006). Unlike more traditional CBT approaches, which tend to focus on modifying
psychological events directly (e.g., by challenging the validity of negative automatic
thoughts), ACT seeks to alter the behavioural inﬂuence of those events through a
combination of mindfulness and values-based behavioural activation strategies (Hayes,
Villatte, Levin, & Hildebrandt, 2011; Hayes et al., 2006).
The stated aim of ACT is to enhance psychological ﬂexibility, which is technically
deﬁned as the ability to contact the present moment fully as a conscious human being, and
to persist or change behaviour in the service of chosen values (Hayes, Strosahl, Bunting,
Twohig, & Wilson, 2004). In simpler terms, ACT seeks to help people pursue and expand
personally valued patterns of behaviour, even while experiencing difﬁcult or unhelpful
thoughts, feelings, sensations, and urges. To enhance psychological ﬂexibility, ACT
interventions target six interrelated therapeutic processes: contact with the present
moment, acceptance, cognitive defusion, self-as-context, values clariﬁcation, and
committed action (Hayes et al., 2006).
A large body of research supports the utility of ACT as a treatment for various clinical
presentations (for reviews see A-Tjak et al., 2015; Graham, Gouick, Krahe, & Gillanders,
2016; Hayes et al., 2006; €
Ost, 2008, 2014; Powers, V€
ording, & Emmelkamp, 2009; Pull,
2008; Ruiz, 2010; Swain, Hancock, Hainsworth, & Bowman, 2013; Veehof, Oskam,
2Cerith S. Waters et al.
Schreurs, & Bohlmeijer, 2011; Vøllestad, Nielsen, & Nielsen, 2012). In the workplace
context, ACT has been translated into brief, skills-based, and group format training
programmes that can be delivered to general working populations (e.g., Brinkborg,
Michanek, Hesser, & Berglund, 2011; Flaxman & Bond, 2006, 2010a; Flaxman, Bond, &
Livheim, 2013). Several previous workplace studies have demonstrated that brief ACT-
based training programmes can elicit signiﬁcant improvements in employees’ general
mental health and reductions in work-related burnout (e.g., Bond & Bunce, 2000;
Brinkborg et al., 2011; Flaxman & Bond, 2010b; Fr€
eli, Djordjevic, Rudman, Livheim, &
Gustavsson, 2015; Lloyd, Bond, & Flaxman, 2013; McConachie, McKenzie, Morris, &
The present study seeks to contribute to this emergent strand of intervention research
and practice in two ways. First, most previous evaluations of ACT-based training in the
workplace have been efﬁcacy studies (i.e., RCTs) that were initiated and orchestrated by
research teams external to the participating organizations. This means that (1) the ACT
interventions being evaluated were typically delivered by external practitioners, who had
been speciﬁcally trained to deliver the study’s intervention protocol, and (2) the
workplace ACT interventions that have been evaluated thus far were (as far as we are
aware) not routinely available to the participating organizations’ employees before or
after the research studies were completed. Notwithstanding the strengths and inﬂuence
of this type of intervention efﬁcacy research, it is important to gather supplementary
evidence of an intervention’s effectiveness within more routine practice settings (e.g.,
Barkham & Margison, 2007; Barkham & Mellor-Clark, 2000, 2003; Barkham et al., 2008;
Borkovec, Echemendia, Ragusea, & Ruiz, 2001; Cahill, Barkham, & Stiles, 2010; Shadish,
Navarro, Matt, & Phillips, 2000).
Accordingly, the ﬁrst aim of this study was to adopt a practice-based approach, by
evaluating a full-day ACT workshop being offered as a routine and integral part of an
organization’s clinical support provision for psychologically distressed staff. This practice-
based approach may help to address calls for research that exhibits greatest relevance to
how therapeutic interventions are likely to be delivered in routine practice settings
(Barkham & Margison, 2007). In addition, by evaluating an ACT programme offered by an
established clinical service for staff, we anticipated attracting a sample of employees with
a clinical level of psychological distress, thereby avoiding the ‘dilution’ effect encountered
in previous studies of ACT in the workplace that have attracted heterogeneous groups of
workers (Bond & Bunce, 2000; Flaxman & Bond, 2010b; see also Bunce, 1997; Bunce &
The second aim of this study was to assess the speciﬁcity of ACT’s putative processes of
change within this clinical practice setting. In particular, we test a central theoretical
assumption of the ACT approach that ACT interventions operate primarily by altering the
function –rather than the form or frequency –of negative or difﬁcult psychological
content (Hayes et al., 2006). To this end, we explore the degree to which beneﬁcial
effects of an ACT workshop on employees’ mental health are related to: (1) a reduced
inﬂuence of difﬁcult psychological content over behaviour (i.e., increased psychological
ﬂexibility); (2) a change in employees’ relationship with their negative or difﬁcult
cognitive and emotional experiences (i.e., reduced cognitive fusion and enhanced
mindfulness skills); or (3) a reduction in the frequency of negative cognitions. Evidence
that an ACT intervention’s beneﬁcial effects are being transmitted through changes in (1)
and/or (2) –and not (3) –would be congruent with ACT theory (Hayes et al., 2006).
We utilized a quasi-controlled design in which health care employees were
allocated in blocks, according to self-referral date, to a 1-day ACT workshop or to a
ACT for distressed health care workers 3
waiting list control group. We predicted that the ACT workshop would lead to
signiﬁcant improvements in the mental health of clinically distressed employees over a
3-month evaluation period. We further hypothesized that the anticipated beneﬁcial
effects of ACT on employees’ mental health would be mediated through improvements
in ‘ACT-consistent’ therapeutic processes (i.e., enhanced psychological ﬂexibility,
cognitive defusion, and/or mindfulness skills), and not via a reduction in the frequency
of negative automatic thoughts.
Participants and procedure
Participants were employees of a large health care organization in Wales, UK. An
advertisement for the ACT intervention was posted on an intranet page by the staff
support service and circulated by email. At the point of self-referral, employees were
placed on a waiting list and received a provisional booking for the ACT workshop, along
with an invitation to participate in the research study. The initial pack sent to interested
employees contained information about the intervention (e.g., basic aims, dates, and
venue), and the research study (e.g., how to provide consent), pre-intervention (baseline)
surveys, and a prepaid envelope for returning completed surveys.There were no
inclusion or exclusion criteria for attending the ACT intervention or participating in the
During the period of the study, a total of 50 employees were booked in to attend the
ACT workshop. Of these 50 employees, 35 (70%) consented to participate in the research,
completed pre-intervention measures, and were allocated to the ACT workshop or to a
waiting list control group. There were no signiﬁcant differences between those who did/
did not consent to participate in level of psychological distress or on any of the collected
demographic variables (i.e., gender, age, job role, job tenure, marital status, or educational
The staff support service’s management committee expressed concern about holding
distressed members of staff on a waiting list for evaluation purposes. In consultation with
this committee, the organization’s research and development (R&D) department, and a
local ethics review panel, it was agreed that allocation to study condition could be
conducted in blocks according to self-referral date. Thus, the ﬁrst eight employees who
had referred themselves for the intervention were allocated to the next batch of ACT
workshops, the next eight were allocated to the waiting list, and so on, until 17
participants had been allocated to the ACT workshop and 18 to the waiting list control
group (see Figure 1 for participant ﬂow through the study). There were no signiﬁcant
differences found on any study or demographic variable between the ACT and control
groups (see Table 1 for more detailed sample characteristics). All study procedures were
approved by the local research ethics committee.
To assess the degree of psychological distress in the sample, each participant’s
baseline caseness score was calculated on the general health questionnaire (GHQ-12).
Using the caseness scoring method, a score of 4 or more on the GHQ-12 indicates a
probable case of minor psychiatric disorder (typically anxiety and/ or depression) in a
working population (e.g., Stride et al., 2007; Wall et al., 1997). Of the 15 participants in
the ACT group who went on to receive the intervention, 14 (93%) had a pre-intervention
GHQ-12 caseness score of 4 or above. Similarly, 13 of the 18 (72%) control group
participants had a baseline GHQ-12 score ≥4. Thus, as anticipated, offering ACT within a
4Cerith S. Waters et al.
clinical service for staff attracted a sample of employees with an above average and
clinically relevant level of psychological distress.
General health questionnaire-12 (GHQ-12; Goldberg & Williams, 1988)
This 12-item scale is one of the most widely used and validated measures of general
psychological distress, deﬁned in terms of cognitions (e.g., worry), emotions (e.g., feeling
constantly under strain), and day-to-day functioning (e.g., feeling able to play a useful part
in things). The Likert scoring method was used for all main analyses (Goldberg et al.,
1997). This method assigns values of 0, 1, 2, and 3 to the GHQ’s four response options.
Higher scores indicate greater psychological distress. The GHQ-12 exhibited high internal
Self-referrals for ACT workshop
during study period (n=50)
Declined to participate (n = 15)
Completer sample (n=14)
ITT sample (n=17)
Lost to follow-up (did not return 3 month
post-intervention measures; n = 3)
Allocated to ACT intervention (n= 17)
♦Received intervention (n=15)
♦Did not receive intervention (no reasons
given; n= 2)
Lost to follow-up (did not return 3 month
post-intervention measures; n = 2)
Allocated to waiting list control group (n=18)
Completer sample (n=16)
ITT sample (n=18)
Received intervention (n=16)
♦Did not receive intervention (no reasons
given; n= 2)
Figure 1. Participant ﬂow.
ACT for distressed health care workers 5
consistency in this study: Cronbach alphas (a) were .91 at pre-intervention and a=.92 at
3 months post-intervention.
Acceptance and action questionnaire–II (AAQ-II; Bond et al., 2011)
The 7-item AAQ-II is a widely used measure of psychological ﬂexibility in the ACT
literature. The scale captures a person’s (lack of) willingness to experience undesirable
psychological content (e.g., ‘I worry about not being able to control my worries and
feelings’) and the extent to which difﬁcult thoughts and feelings are having an unhelpful
inﬂuence over behaviour (e.g., ‘Worries get in the way of my success’). In this study, the
scale was reverse-scored, so that higher scores indicated greater psychological ﬂexibility.
Alpha coefﬁcients were a=.84 at pre-intervention and a=.88 at 3 months
Five facet mindfulness questionnaire (FFMQ; Baer, Smith, Hopkins, Krietemeyer, & Toney, 2006)
This 39-item scale measures a combination of ﬁve mindfulness skill facets: observing (e.g.,
‘When I’m walking, I deliberately notice the sensations of my body moving’); describing
(labelling with words; e.g., ‘I’m good at ﬁnding the words to describe my feelings’); acting
with awareness (e.g., ‘I ﬁnd it difﬁcult to stay focused on what’s happening in the
present’); non-judging of experience (e.g., ‘I make judgments about whether my
thoughts are good or bad’); and non-reactivity to difﬁcult inner experience (e.g., ‘When I
have distressing thoughts or images, I am able just to notice them without reacting’). In the
this study, Cronbach alphas for FFMQ total score were a=.89 at pre-intervention and
a=.94 at 3 months post-intervention. A higher score indicates a greater degree of
Automatic thoughts questionnaire (ATQ;Hollon & Kendall, 1980)
The ATQ is a 30-item scale of negative (depressogenic) cognitive content (e.g., ‘I can’t get
things together’; ‘I’m a failure’). In its original form, the ATQ measures the frequency
(ATQ-F) of such thoughts, with a response scale ranging from 1 (not at all) to 5 (all the
time). ACT researchers extended the original scale to create a measure of believability in
negative thought content (ATQ-B; Zettle & Hayes, 1986). The ATQ-B uses the same set of
Table 1. Completer sample baseline (Pre-intervention) characteristics
Age (Myears/SD) 38.2 (10.4) 40.9 (9.0) 39.7 (9.6)
Gender (% female) 80 88 84
Married/Partner (%) 60 75 68
University degree (%) 80 56 68
Nursing (%) 60 63 61
Allied health professional (%) 27 6 16
Non-clinical job role (%) 13 31 23
Role Banding (median/range) 5 (4–7) 5 (2–8) 5 (2–8)
Years worked for org (Myears/SD) 10.6 (10.8) 14.6 (9.1) 12.7 (10.0)
6Cerith S. Waters et al.
30 negative automatic thoughts, but respondents are asked to rate how strongly, if at all,
they believe the listed thoughts, when they occur (with a response scale ranging from 1
not at all to 5 totally). The ATQ-B is used as a proxy measure of cognitive fusion (Hayes
et al., 2006). In the current sample, reliability coefﬁcients for the ATQ-F were a=.95 at
pre-intervention and a=.98 at 3 months post-intervention; ATQ-B a=.94 at
pre-intervention and a=.97 at 3 months post-intervention.
The 1-day ACT workshop was already being routinely delivered by the organization’s in-
house staff support service on frequent occasions, between 9 am and 5 pm, to groups of
between 8 and 12 participants. All of the workshops evaluated in this study were delivered
by the same in-house counsellor/ ACT therapist, who had extensive experience of
delivering individual and group psychotherapy. The therapist had previously attended
training in an ACT for the workplace by one of the programme’s originators and received
regular clinical supervision throughout the study.
The content of the workshop was based on an ACT for the workplace training
approach described by Flaxman and Bond (2006; see also Flaxman & Bond, 2010a;
Flaxman et al., 2013). The workshop sought to offer participants an integration of
mindfulness and values-based action skills. Participants were introduced to various
techniques that were designed to: (1) raise awareness of psychological barriers (such as
‘unhelpful’ thoughts) to engagement in personally valued action; (2) undermine the use of
internal control efforts as a way of managing unwanted thoughts and emotions; (3) raise
awareness of the distinction between strategies that work inside the skin/ outside the
skin; (4) cultivate defusion through mindfulness practices that involve noticing the
process of thinking; and (5) help participants clarify personal values that could be used as a
meaningful guide to daily action. The trainer made use of two of ACT’s well-known
metaphors –passengers on the bus and the polygraph metaphor (Hayes, Strosahl, &
Wilson, 1999) –to help convey key messages and summarize the approach. Towards the
end of the workshop, participants were invited to reﬂect and share within the group how
they might transfer the learning and further cultivate mindfulness and valuing skills, in
their daily lives.
Data were analysed in two stages. First, we examined the effects of the ACT
intervention on employees’ general mental health (i.e., GHQ-12), psychological
ﬂexibility (AAQ-II), mindfulness skills (FFMQ), and on the frequency (ATQ-F) and
believability (ATQ-B) of negative automatic thoughts across the 3-month evaluation
period. These outcome analyses were performed on an intent-to-treat (ITT) basis,
following multiple imputation (MI) of missing data (using SPSS version 22 multiple
imputation procedure). All 35 participants who had been allocated to condition were
included in the ITT analyses. Results were pooled across ﬁve imputations for each
variable. Because SPSS reports pooled MI results for linear regression but not ANCOVA,
we present unstandardized regression coefﬁcients for each between-group comparison
at 3 months post-intervention, controlling for the relevant pre-intervention scores.
Second, we computed a series of bootstrapped multiple mediation models using the
PROCESS macro and syntax for SPSS (Hayes, 2013; Preacher & Hayes, 2008). This
bootstrapped analysis was based on 5000 iterations and was utilized to test for indirect
ACT for distressed health care workers 7
effects of the ACT intervention on employees’ mental health via ACT-consistent processes
of change (i.e., psychological ﬂexibility, defusion, and/or mindfulness skills), above and
beyond any change in the frequency of negative automatic thinking.
As indicated in Figure 1, two participants allocated to the ACT group did not attend the
intervention. One other participant in the ACT group attended the workshop but failed to
return post-intervention measures. In the control group, two participants did not return
post-intervention measures. As a result, the completer sample comprised of 30
ITT outcome analyses
Effect of ACT on employees’ mental health (GHQ-12)
Table 2 displays pooled descriptive statistics for the ITT sample (N=35), along with
between-group effects evident at 3 months post-intervention (after controlling for pre-
intervention scores on the variable of interest). Consistent with our ﬁrst hypothesis, the
ACT group reported a signiﬁcantly lower level of psychological distress at 3 months post-
intervention compared to the control group: B =9.39, p<.001, d=1.41.
Table 2. Intention-to-treat (ITT) sample means, standard deviations, and between-group effects at
3 months post-intervention
(n=18) Between-group effects
MSDMSD BSE t
Pre-intervention 21.71 5.29 20.28 6.94
Post-intervention 11.29 5.10 19.87 6.92 9.39 1.82 5.16***
Pre-intervention 26.41 6.86 25.67 9.41
Post-intervention 32.58 9.0 25.73 8.99 6.40 2.90 2.20*
Pre-intervention 111.06 21.21 113.72 13.24
Post-intervention 124.70 19.23 111.74 13.45 14.62 4.43 3.30**
Pre-intervention 79.53 24.97 81.28 25.81
Post-intervention 61.18 30.42 79.51 31.78 16.54 7.72 2.14*
Pre-intervention 76.35 26.26 79.44 23.69
Post-intervention 68.87 31.42 80.32 32.61 8.81 9.02 .98
Notes.N=35. Means and SDs were pooled across ﬁve imputations.
*p<.05; **p<.01; ***p<.001.
Pooled (unstandardized) regression coefﬁcients (B) testing differences between the ACT and control
group at 3 months post-intervention, while controlling for pre-intervention scores.
8Cerith S. Waters et al.
The clinical relevance of this improvement on the GHQ-12 was assessed using Jacobson
et al.’s two criteria for establishing clinically signiﬁcant change (e.g., Jacobson, Roberts,
Berns, & McGlinchey, 1999; Jacobson & Truax, 1991). At 3 months post-intervention,
50% (7 of 14) of the initially distressed participants who had attended the ACT
intervention met the criteria for reliable and clinically meaningful change and were
therefore deﬁned as ‘recovered’. The remaining 50% of ACT participants were classiﬁed as
. In contrast, none of the initially distressed control group participants exhibited
clinically signiﬁcant improvement across the same 3-month assessment period. One
participant in the control group reported a signiﬁcant increase on the GHQ-12 across the
study period and was classiﬁed as ‘reliably deteriorated’.
The control group participants subsequently received the intervention following
3 months on the waiting list. Three months after receiving the same ACT intervention,
nine of the 13 initially distressed participants (69%) who had been on the waiting list met
the criteria for clinically signiﬁcant change on the GHQ-12 and were classiﬁed as
recovered. The remaining four participants were classiﬁed as the same.
Effects of ACT on psychological ﬂexibility (AAQ-II), mindfulness (FFMQ), defusion (ATQ-B), and
frequency of negative automatic thoughts (ATQ-F)
The effects of ACT on the potential process of change variables were assessed in the ITT
sample. As shown in Table 2, at 3 months post-intervention, participants in the ACT
condition had signiﬁcantly higher levels of psychological ﬂexibility (B =6.40, p=.03),
mindfulness skills (B =14.62, p=.001) and exhibited less fusion with negative
cognitions (B =16.54, p=.04). In contrast, the ACT workshop did not result in a
statistically signiﬁcant reduction in the frequency of negative automatic thoughts
(B =8.81, ns). The same pattern of results was found in the ITT and the completer data,
suggesting that participant drop-out had little impact on study ﬁndings. Table 3 displays
the correlations between the study variables.
Bootstrapped mediation analyses
To test the hypothesis that ACT operates primarily by altering the function of difﬁcult
thoughts and feelings, and not by altering their form or frequency, we constructed three
bootstrapped multiple mediator models. In these models, we tested for indirect effects of
the ACT workshop on employees’ mental health (i.e., pre- to post-change on the GHQ-12)
through each of the ACT-consistent processes, while controlling for any change in the
frequency of negative cognitions (i.e., the ATQ-F).
Table 4 summarizes the results. Only one of the three models showed statistically
signiﬁcant total and speciﬁc indirect effects. There was a speciﬁc indirect effect of the ACT
intervention on the GHQ-12 via an increase in employees’ mindfulness skills from pre- to
post-intervention: estimate =2.42, BCa 95% [CI .42, 7.21]. In addition, there was a
signiﬁcant contrast comparing the relative inﬂuence of change in mindfulness skills and
change in the frequency of negative cognitions: estimate =2.54, BCa 95% [CI .17, 9.89].
This latter ﬁnding suggests that ACT’s effect on employees’ mental health via an increase
in mindfulness was signiﬁcantly larger than the effect occurring through a reduction in the
frequency of negative thoughts.
Given that mindfulness was found to be the most inﬂuential mediator of GHQ-12
change, we explored whether the ACT workshop was having a particularly strong effect
ACT for distressed health care workers 9
on a subset of the FFMQ’s facets. We found signiﬁcant group by time interaction effects
only for the FFMQ’s observing and non-reactivity subscales. In addition, at 3 months
post-intervention (while controlling for pre-intervention scores on each facet), the ACT
group had signiﬁcantly higher scores than the control group on observing (B =3.53,
SE =1.60, t=2.21, p=.04) and non-reactivity (B =3.05, SE =1.01, t=3.01,
Table 3. Bivariate correlations between study variables
1. Distress pre-intervention –
2. Distress post .39 –
3. Flexibility pre-intervention .61 .39 –
4. Flexibility post-intervention .26 .59 .54 –
5. Mindfulness pre-intervention .44 .29 .43 .49 –
6. Mindfulness post-intervention .24 .57 .29 .65 .58 –
7. Fusion pre-intervention .25 .40 .67 .64 .43 .33 –
8. Fusion post-intervention .21 .51 .54 .77 .47 .58 .81 –
9. Cognitions pre-intervention .27 .37 .62 .54 .38 .28 .93 .77 –
10. Cognitions post-intervention .31 .43 .45 .70 .51 .62 .66 .86 .67 –
Note. Based on ITT data (N=35). Correlations were pooled across ﬁve imputations. Distress =psy-
chological distress (GHQ-12); ﬂexibility =psychological ﬂexibility (AAQ-II); mindfulness (FFMQ total
score); fusion =cognitive fusion (ATQ-B); cognitions =frequency of negative cognitions (ATQ-F).
Coefﬁcients ≥.37 in the ITT data set were statistically signiﬁcant.
Table 4. Bootstrapped multiple mediator models testing indirect effects of ACT on employees’ mental
Bootstrap estimate BCa 95% CI
Estimate SE Lower Upper
Psychological ﬂexibility (AAQ-II) 3.0 2.19 0.91 6.58
Negative cognitions (ATQ-F) 0.40 0.88 2.95 0.72
Total indirect effect 2.60 1.78 1.56 5.06
Contrast (AAQ-II vs. ATQ-F) 3.39 2.83 1.65 8.64
Mindfulness (FFMQ) 2.42 1.55 0.42 7.21
Negative cognitions (ATQ-F) 0.12 0.93 5.57 0.56
Total indirect effect 2.30 1.46 0.02 5.75
Contrast (FFMQ vs. ATQ-F) 2.54 2.10 0.17 9.89
Cognitive fusion (ATQ-B) 2.67 3.44 9.86 3.27
Negative cognitions (ATQ-F) 1.77 2.97 1.89 9.15
Total indirect effect 0.90 1.39 3.76 2.02
Contrast (ATQ-B vs. ATQ-F) –4.43 6.28 18.50 4.51
Note. Pre-intervention scores on each variable were entered as covariates in each model. BCa =bias-
corrected and accelerated conﬁdence intervals. Results based on 5,000 bootstrap samples. Rows in bold
indicate signiﬁcant indirect effects or contrasts.
10 Cerith S. Waters et al.
p=.006). We therefore entered the observing and non-reactivity facets together in a
multiple mediator model alongside the ATQ-F (see Table 5). This model’s total indirect
effect was statistically signiﬁcant. There were also signiﬁcant speciﬁc indirect effects of
ACT on employees’ mental health via the increase in observing (estimate =1.72, BCa 95%
CI .07, 5.09) and via the increase in non-reactivity (estimate =2.52, BCa 95% CI .12, 6.45).
The speciﬁc indirect effect of ACT on the GHQ-12 via change in the frequency of negative
thinking was not signiﬁcant.
The aims of this study were to: (1) assess the effects a 1-day ACT workshop being delivered
in a routine practice setting for clinically distressed health care employees and (2) explore
the speciﬁcity of ACT’s processes of change. Our results indicate that ACT was effective in
improving the general mental health of a sample of self-referred employees across a
3-month evaluation period. Moreover, and despite the brevity of the intervention,
between one-half and two-thirds of initially distressed employees who attended the ACT
workshop exhibited clinically signiﬁcant improvement on the GHQ-12. This is an
encouraging ﬁnding, given the prevalence (and costs) of common mental health
problems, and poor access-to-treatment rates, being found among working populations
(Hardy et al., 2003; Hilton et al., 2008).
Our outcome ﬁndings are consistent with previous studies of ACT in workplace
settings, which have also reported moderate to large improvements in mental health
(including on the GHQ-12) following similarly brief ACT-based training programmes (e.g.,
Brinkborg et al., 2011; Flaxman & Bond, 2010b,c). Our ﬁndings make a novel
contribution to this strand of research, by showing that similar effects are found when
ACT is delivered within a routine staff support setting, and not just when ACT is being
offered to organizations as part of standalone and externally orchestrated RCTs.
It is worth noting how our practice-based evaluation approach differs from previous
studies of ACT in the workplace. By offering ACT via a clinical support service for staff, we
attracted a sample of employees with a signiﬁcantly higher average level of psychological
distress than has been observed in previous studies (Bond & Bunce, 2000; Brinkborg
et al., 2011). Flaxman and Bond (2010b) noted that around 50% of employees recruited to
Table 5. Bootstrapped multiple mediator model testing indirect effects of ACT on employees’ mental
health (GHQ-12) via observing and non-reactivity
Bootstrap estimate BCa 95% CI
Estimate SE Lower Upper
Observing 1.72 1.18 0.07 5.09
Non-reactivity 2.52 1.58 0.12 6.45
Negative cognitions (ATQ-F) 0.20 0.95 2.52 1.41
Total indirect effect 4.44 2.0 .66 8.27
Contrast (observe vs. ATQ-F) 1.52 1.60 –.49 6.35
Contrast (non-react vs. ATQ-F) 2.32 1.81 7.75 .10
Note. Pre-intervention scores on each variable were entered as covariates in each model. BCa =bias-
corrected and accelerated conﬁdence intervals. Results based on 5,000 bootstrap samples. Rows in bold
indicate signiﬁcant indirect effects or contrasts.
ACT for distressed health care workers 11
a similar ACT worksite intervention offered as part of an RCT were presenting with
clinically relevant levels of psychological distress (compared to 90% in the present study).
Thus, we believe that offering this type of ACT programme within a workplace clinical
service is a useful way of attracting those employees who are most in need of
A second contribution of this study stems from our assessment of various potential
psychological processes of change when a 1-day ACT workshop is offered in a staff
support setting. Consistent with ACT’s underlying theory, we found that the ACT
workshop resulted in signiﬁcant improvements in psychological ﬂexibility, defusion, and
mindfulness, but had less impact on the frequency with which distressed employees were
experiencing negative automatic thoughts. Moreover, when we allowed each of the ACT-
consistent processes to ‘compete’ with change in the frequency of negative thinking in
multiple mediator models, ACT was found to be improving mental health primarily by
strengthening employees’ mindfulness skills (i.e., via pre- to post-change on the FFMQ).
This ﬁnding suggests that ACT, similar to other mindfulness-based interventions (MBIs),
works in part by modifying people’s relationship with negative or difﬁcult psychological
The signiﬁcant indirect effect through mindfulness also lends some support to those
who argue that the various MBI approaches (such as ACT, MBCT, and MBSR) –though
underpinned by different theories and characterized by different techniques –are
targeting some fundamentally similar psychological processes (e.g., Baer, 2010; Hayes
et al., 2011). In terms of practicality, it is noteworthy that workplace ACT programmes
are typically briefer than some other workplace MBIs (e.g., the 8-week MBSR programme)
and involve less formal meditation practice. Thus, we tentatively suggest that ACT may
offer an alternative for some distressed employees who may beneﬁt from enhancing their
mindfulness skills but are unlikely (or unable) to engage in more lengthy meditation-based
interventions. One useful avenue for future research in this area would be to directly
compare the effects of brief ACT programmes with more elaborate MBIs in a workplace
Further analyses revealed that two speciﬁc mindfulness skills seemed to be operating
as especially inﬂuential processes of change in the present study: an increased ability to
notice bodily sensations and sensory input across the ﬁve senses (i.e., the FFMQ’s
observing skill facet), and the development of a less reactive stance towards difﬁcult
thoughts and feelings (i.e., the FFMQ’s non-reactivity skill facet). At a theoretical level, it is
not difﬁcult to see the congruence between these two mindful skill facets and the set of
mindfulness/acceptance processes in ACT’s model of psychological ﬂexibility (Hayes
et al., 2004, 2006). Speciﬁcally, the capacity to observe one’s direct, present-moment
experience mirrors ACT’s ‘aware’ processes (i.e., present-moment awareness and self-as-
context), while the non-reactivity facet aligns with ACT’s ‘open’ processes (i.e., defusion
and acceptance; Hayes et al., 2011; see also Baer et al., 2006).
From a more practical perspective, the ﬁnding that the ACT workshop was inﬂuencing
these two mindful skills supports the use of techniques that raise people’s awareness of
present-moment physical sensations (e.g., by learning to shift one’s attention into the
body), as well as the various strategies ACT employs to help people notice that they do not
have to react to, get caught up in, or be overly controlled by unhelpful cognitions, urges,
or emotions, which can instead come to be viewed as a natural part of the human
condition (Flaxman et al., 2013).
When interpreting these ﬁndings, it is important to note several limitations in the
design of the current study. Our sample size is relatively small, and our study provides only
12 Cerith S. Waters et al.
a pilot and snapshot evaluation of an ACT programme that was being delivered to larger
numbers of employees within the host organization. Although we were able to make use
of a waiting list comparison group, participants were not randomly allocated to condition.
This may detract from the study’s internal validity. However, we found no signiﬁcant
differences between the ACT and control groups on any of the study variables. Our
method of recruitment bore a close resemblance to how the staff support service
operated, with employees being allocated to ACT workshops until they were full, and
others placed on a waiting list and given dates for the next round of training in a few
months’ time. Thus, while the non-randomized design may reduce the study’s internal
validity, we believe the study exhibits strong external validity. By nesting the research
within the routine clinical service, we hope to have addressed calls for evaluations of
psychological interventions under usual service conditions (Barkham & Margison, 2007;
Shadish et al., 2000).
The study design is further limited by the lack of an active control condition. As a
result, any non-speciﬁc intervention effects were not controlled for. It is possible that
the improvement in mental health in the ACT condition was partly attributable to
feelings of group support, the interpersonal warmth of the therapist, or participants’
own individual characteristics (e.g., motivation to change). In addition, the same
therapist delivered all the ACT workshops being evaluated; thus, we cannot rule out
the possibility that the therapist had particular skills or characteristics that may have
inﬂuenced the outcomes.
Because the study focuses on only two assessment occasions, mediator and outcome
variables were measured at the same point in time. A stronger demonstration of mediation
would need to show that hypothesized mediating variables are changing prior to change
in the outcome. Thus, future studies of ACT in the workplace would beneﬁt from having
additional and repeated measurement occasions in the ﬁrst few weeks following the
workshop (cf. Arch, Wolitsky-Taylor, Eifert, & Craske, 2012; Gloster et al., 2017; Hayes,
Orsillo, & Roemer, 2010).
Another limitation is that we focused primarily on ACT’s mindfulness and acceptance
processes and not on the values and committed action elements of the ACT model.
Although we included a general measure of psychological ﬂexibility, we did not examine
whether the ACT workshop resulted in an increase in employees’ capacity to engage in
values-based behaviour. Recent research has demonstrated that values-based action can
function as an inﬂuential process of change during longer ACT treatments (Gloster et al.,
2017). Hence, future studies of ACT in the workplace may beneﬁt from including
measures of values-based behavioural activation. Finally, we used a ‘proxy’ measure to
capture cognitive defusion (operationalized as degree of belief in negative thought
content). Although other ACT researchers have used the ATQ-B for the same purpose (see
Hayes et al., 2006 for a review), it would be useful to assess the impact of this type of ACT-
based training on more recently developed measures of defusion (e.g., Gillanders et al.,
Despite these methodological limitations, the present study provides some prelim-
inary practice-based evidence that a brief ACT intervention can be effective in improving
the mental health of distressed health care employees. It is encouraging that, when
evaluated within a more routine clinical (staff support) service, ACT’s beneﬁcial inﬂuence
on employees’ mental health was found to be equivalent to that reported in previous
worksite RCTs. In addition, we found some support for the notion that ACT’s effects on
mental health are transmitted (at least in part) via mindfulness and acceptance processes,
and not via change in the form or frequency of negative cognitions. We hope that these
ACT for distressed health care workers 13
promising ﬁndings encourage other researchers to conduct evaluations of ACT-based
interventions as they are being delivered in real-world practice settings.
We extend our thanks to the staff at the Employee Wellbeing Service for supporting this
research study and our gratitude to the participants who so generously gave up their time
during a stressful period in their lives.
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Received 8 February 2017; revised version received 30 June 2017
ACT for distressed health care workers 17