A continuum exists between the testing of treatments under traditional, highly controlled circumstances in which it is determined whether the treatment is efficacious (i.e., efficacy trials) and the application of these treatments under more complicated or ‘real-world’ conditions (effectiveness trials). There continues to be a need to test the effectiveness of trauma-focused treatments delivered in community settings. There is increasing support for treatment of chronic problems such as posttraumatic stress disorder (PTSD) in routine clinical care settings (e.g., Foa et al., Reference Foa, Hembree, Cahill, Rauch, Riggs, Feeny and Yadin2005; Forbes et al., Reference Forbes, Lloyd, Nixon, Elliott, Varker, Perry and Creamer2012; Schnurr et al., Reference Schnurr, Friedman, Engel, Foa, Shea, Chow and Bernardy2007). However, our knowledge of treating recent stress reactions as seen in acute stress disorder (ASD) in such settings is very limited. This is particularly the case in sexual assault survivors, who experience high levels of acute stress symptoms (Elklit & Christiansen, Reference Elklit and Christiansen2010; Resick Reference Resick1988; Rothbaum et al., Reference Rothbaum, Foa, Riggs, Murdock and Walsh1992; Steenkamp, Dickstein, Salters-Pedneault, Hofmann, & Litz, Reference Steenkamp, Dickstein, Salters-Pedneault, Hofmann and Litz2012).

Trauma-focused therapies are recommended frontline interventions for acute and posttraumatic stress disorder (Australian Centre for Posttraumatic Mental Health [ACPMH], 2013; National Institute for Clinical Excellence [NICE], 2005). Although symptoms can resolve without formal intervention in the weeks following trauma, treatment can be considered when ASD is present and causing distress (ACPMH, 2013). There is a growing evidence base for trauma-focused CBT methods for ASD (see Koucky, Galovski, & Nixon, Reference Koucky, Galovski and Nixon2012, for review); however, the bulk of this research has either come out of one treatment centre (that of Richard Bryant and colleagues; however, see also Foa, Hearst-Ikeda, & Perry, Reference Foa, Hearst-Ikeda and Perry1995; Foa, Zoellner, & Feeny, Reference Foa, Zoellner and Feeny2006; Rothbaum et al., Reference Rothbaum, Kearns, Price, Malcoun, Davis, Ressler and Houry2012). Studies to date have comprised mixed trauma rather than purely sexual assault samples, and generally studies have been conducted in expert treatment centres and/or with clinicians highly proficient in and with strong allegiance to trauma-focused CBT approaches.

Recently, a condensed, six-session version of the highly effective PTSD treatment, cognitive processing therapy (CPT; Resick et al., Reference Resick, Galovski, Uhlmansiek, Scher, Clum and Young-Xu2008; Resick, Nishith, Weaver, Astin, & Feuer, Reference Resick, Nishith, Weaver, Astin and Feuer2002), has shown promise for treating ASD in a mixed assault sample (Nixon, Reference Nixon2012). The present article examines the effectiveness of CPT compared with active TAU for survivors of recent sexual assault with ASD. Therapy was delivered by community clinicians working in a sexual assault centre, and clients were assessed at posttreatment as well as 3 months, 6 months, and 12 months following treatment. We did not use a waitlist control group given prior ASD studies have shown active treatment results in greater change than such control groups (Bryant et al., Reference Bryant, Mastrodomenico, Felmingham, Hopwood, Kenny, Kandris and Creamer2008; Foa et al., Reference Foa, Hearst-Ikeda and Perry1995; Foa et al., Reference Foa, Zoellner and Feeny2006), and the service did not allow this design due to ethical concerns of delaying treatment for their clients. We predicted that both interventions would result in sizeable reductions in posttrauma symptom severity and depression but that these changes would be more pronounced in the CPT group.

At this time no effectiveness trials of ASD treatment have been conducted in a community mental health setting, let alone for sexual assault survivors with ASD. Our study addresses this limitation. The importance of this work is underscored by prospective studies that have found that in the month after sexual assault, approximately 60–78% of women have clinically significant acute stress symptoms (Elklit & Christiansen, Reference Elklit and Christiansen2010; Resick, Reference Resick1988; Rothbaum et al., Reference Rothbaum, Foa, Riggs, Murdock and Walsh1992; Steenkamp et al., Reference Steenkamp, Dickstein, Salters-Pedneault, Hofmann and Litz2012). In these largely non-treatment seeking samples, between 35–55% had probable PTSD 3–4 months post-assault, underscoring the consequences of this high impact trauma. Unlike other trauma samples where a sizeable number of survivors might show a resilience trajectory following trauma (i.e., mild initial symptoms followed by good recovery or generally low symptoms; e.g., deRoon-Cassini, Mancini, Rusch, & Bonanno, Reference deRoon-Cassini, Mancini, Rusch and Bonanno2010; O'Donnell, Elliot, Lau, & Creamer, Reference O'Donnell, Elliot, Lau and Creamer2007), sexual assault is associated with high levels of symptoms that persist for a significant number of individuals. More recently, Steenkamp et al. (Reference Steenkamp, Dickstein, Salters-Pedneault, Hofmann and Litz2012) observed that only 30% of their sample could be characterised as fitting into a group considered to have demonstrated substantial recovery by 4 months posttrauma. There is therefore a need to continue to test interventions for recent sexual assault survivors who present to community mental health.

Despite trauma-focused therapies being recommended frontline interventions, there is also evidence historically that trauma-focused intervention was not used as widely as hoped (Becker, Zayfert, & Anderson, Reference Becker, Zayfert and Anderson2004; Russell & Silver, Reference Russell and Silver2007). However, a number of dissemination and effectiveness trials have demonstrated that interventions with a trauma focus — in particular, cognitive-behavioural therapy (CPT) interventions for PTSD — can be successfully used in routine clinical care settings (e.g., Foa et al., Reference Foa, Hembree, Cahill, Rauch, Riggs, Feeny and Yadin2005; Forbes et al., Reference Forbes, Lloyd, Nixon, Elliott, Varker, Perry and Creamer2012; Schnurr et al., Reference Schnurr, Friedman, Engel, Foa, Shea, Chow and Bernardy2007).

Although there is a growing number of efficacy studies supporting the use of CBT for ASDFootnote ¹ and evidence that associated comorbidity also reduces, such as depressive symptoms (see Koucky et al., Reference Koucky, Galovski and Nixon2012, for review), the bulk of this evidence has come from one research laboratory (Bryant, Harvey, Dang, Sackville, & Basten, Reference Bryant, Harvey, Dang, Sackville and Basten1998; Bryant et al., Reference Bryant, Mastrodomenico, Felmingham, Hopwood, Kenny, Kandris and Creamer2008; Bryant, Moulds, Guthrie, & Nixon, Reference Bryant, Moulds, Guthrie and Nixon2003, Reference Bryant, Moulds, Guthrie and Nixon2005; Bryant, Sackville, Dang, Moulds, & Guthrie, Reference Bryant, Sackville, Dang, Moulds and Guthrie1999, although see also Rothbaum et al., Reference Rothbaum, Kearns, Price, Malcoun, Davis, Ressler and Houry2012), where the samples typically comprise both motor vehicle accident and non-sexual assault survivors. The lack of research with other populations remains a limitation given a recent meta-analysis suggests that of the early intervention studies to date, larger effect sizes are associated with traffic-accident survivors relative to other trauma types (Kliem & Kröger, Reference Kliem and Kröger2013). Two acute PTSD/ASD studies have included sexual assault and non-sexual assault participants (Foa et al, Reference Foa, Hearst-Ikeda and Perry1995; Foa et al., Reference Foa, Zoellner and Feeny2006). These studies observed that at posttreatment, CBT seemed to hasten recovery relative to waitlist (in a non-randomised design; Foa et al., Reference Foa, Hearst-Ikeda and Perry1995) and relative to supportive counselling (Foa et al., Reference Foa, Zoellner and Feeny2006). Foa et al. (Reference Foa, Zoellner and Feeny2006) observed that by 9-month follow-up, few differences were observed between CBT, supportive counselling, and an assessment control condition. However, these findings may also be explained by reduced homework requirements in CBT and the therapeutic effects of the assessment control condition (see Foa et al., Reference Foa, Zoellner and Feeny2006, and Nixon, Reference Nixon2012, for further discussion). At this time there is support for the efficacy of CBT with a trauma-focus for ASD, although the majority of this evidence comes from non-sexual assault samples.

There are two significant gaps in our current knowledge of the optimal methods to treat acute stress relevant to the present study. First, the effectiveness of treatment for ASD in routine community mental health settings is largely unknown, especially for recent sexual assault survivors. To date, the majority of multi-session treatment studies have been conducted in university or research centres and/or with clinicians highly proficient in and with strong allegiance to trauma-focused CBT approaches. Second, consistent with research in relation to clinicians’ attitudes to treating posttraumatic stress in general (Becker et al., Reference Becker, Zayfert and Anderson2004), it is our experience that the proposal of delivering CBT to recent sexual assault survivors can sometimes be met with resistance by clinicians who may have concerns regarding re-traumatisation of clients and exacerbation of symptoms, and in the context of manualised therapies, may see such approaches as interfering with establishing therapeutic alliance. It is important to note these fears are unfounded with no reports of serious adverse events (e.g., self-harm) in ASD trials (e.g., Bryant et al., Reference Bryant, Mastrodomenico, Felmingham, Hopwood, Kenny, Kandris and Creamer2008; Foa et al., Reference Foa, Zoellner and Feeny2006), and PTSD studies indicate working alliance is not compromised in manualised approaches relative to unstructured therapy (e.g., Forbes et al., Reference Forbes, Lloyd, Nixon, Elliott, Varker, Perry and Creamer2012).

The primary goals of the present study were several fold: (1) to further evaluate the efficacy of an abbreviated format of a trauma-focused CBT approach, cognitive processing therapy (CPT), that has showed promise in an initial trial (Nixon, Reference Nixon2012); (2) to examine its efficacy in a wholly sexual assault sample; and (3) to examine whether CPT can be used effectively within a community sexual assault centre where therapy was delivered by non-CBT oriented, non-selected therapists to routine clients.

CPT is typically a 12-session approach, originally designed for the treatment of chronic PTSD following sexual assault. It has demonstrated efficacy in a number of randomised trials with interpersonal and combat trauma samples and also significantly reduces depression symptoms (Chard, Reference Chard2005; Monson et al., Reference Monson, Schnurr, Resick, Friedman, Young-Xu and Stevens2006; Resick & Schnicke, Reference Resick and Schnicke1992; Resick et al., Reference Resick, Galovski, Uhlmansiek, Scher, Clum and Young-Xu2008; Resick et al., Reference Resick, Nishith, Weaver, Astin and Feuer2002). More recently, an effectiveness trial conducted with a veteran sample in routine care found it to be superior to TAU (Forbes et al., Reference Forbes, Lloyd, Nixon, Elliott, Varker, Perry and Creamer2012). Treatment of ASD typically involves 4–6 sessions of CBT (e.g., Foa et al., Reference Foa, Hearst-Ikeda and Perry1995; Foa et al., Reference Foa, Zoellner and Feeny2006; Bryant, Moulds, Guthrie, & Nixon, Reference Bryant, Moulds, Guthrie and Nixon2003, Reference Bryant, Moulds, Guthrie and Nixon2005; Bryant et al., Reference Bryant, Mastrodomenico, Felmingham, Hopwood, Kenny, Kandris and Creamer2008), and the treatment manuals of Bryant and colleagues use materials from the CPT manual. In a pilot study, an abbreviated format of CPT (six sessions) has been shown to be well tolerated by clients exposed to recent trauma and resulted in large reductions in PTSD symptoms when used with (predominantly) non-sexual assault victims (Nixon, Reference Nixon2012). Whether these positive outcomes can be replicated in routine clinical care with recent trauma victims is unknown. Interestingly, the call to use evidence-based treatments in routine clinical care has been questioned. Arguments have been made that the evidence for the superiority of evidence-based treatments is confounded by comparison with ‘treatment as usual’ that has in fact included only minimal therapeutic contact or where TAU therapists were proscribed from employing certain techniques (Benish, Imel, & Wampold, Reference Benish, Imel and Wampold2008; for debates, see Ehlers et al., Reference Ehlers, Bisson, Clark, Creamer, Pilling, Richards and Yule2010, and Wampold et al., Reference Wampold, Imel, Laska, Benish, Miller, Flückiger and Budge2010). There is a need for clear documentation that comparison therapies constitute real and active therapy (e.g., in Forbes et al., Reference Forbes, Lloyd, Nixon, Elliott, Varker, Perry and Creamer2012, TAU was not recorded thus could not be checked the same way that CPT was).

In summary, the present article examines the effectiveness of CPT compared with active TAU for survivors of recent sexual assault with ASD. Therapy was delivered by community clinicians working in a sexual assault centre, and clients were assessed at posttreatment as well as 3 months, 6 months, and 12 months following treatment. We predicted that both interventions would result in sizeable reductions in posttrauma symptom severity and depression but that these changes would be more pronounced in the CPT group.

MethodFootnote ²

Participants

Consecutive clients seeking treatment at the Yarrow Place Rape and Sexual Assault Crisis Centre in Adelaide between June 2008 and April 2011 were considered for the study. Demographic and relevant background is summarised in Table 1. Inclusion criteria consisted of clients being 18 years or older who had experienced rape or sexual assault in the past month and were able to attend face-to-face counselling. Clients had to meet criteria for ASD, and for those taking psychotropic medication this had to be stable for the 4-week period prior to beginning therapy. Clients with uncontrolled psychosis, current substance dependence requiring immediate attention, insufficient English, significant cognitive impairment or disability, significant suicide risk, or ongoing traumatisation (e.g., being stalked) were excluded. Clinical judgment was used to determine whether clients met exclusion criteria, and typically these clients were referred on to further specialist services. All participants provided written informed consent approved by the relevant hospital ethics committee.

TABLE 1 Participant Baseline Characteristics

Note: Some dfs vary due to missing data and percentages are rounded. CPT = Cognitive processing therapy; TAU = Treatment as usual; FET = Fisher's Exact Test.

A total of 158 clients were considered for the study (see Figure 1 for full details of exclusion). The most common reason for exclusion was intellectual/cognitive disability (n = 24), suicide risk (n = 21), and a number of otherwise eligible participants could not make themselves available to be assessed within 4 weeks of their trauma (n = 22). Of those eligible for the study, 82% (n = 47) agreed to participate in the research trial, suggesting that clinical and research exclusion criteria aside, the sample entered into the study was fairly representative of the service's client group. Of the 47 participants randomised to treatment, 25 were allocated to CPT and 22 to TAU (allocation to group was broken after randomisation on two occasions due to therapist unavailability in the TAU condition, hence unequal numbersFootnote ³ ). One participant was withdrawn from the CPT due to a life-threatening illness requiring immediate treatment, leaving 24 in that group. Cessation of funding precluded the reaching of the original target sample size, resulting in lower power being achieved (discussed further in Statistical Methods). As can be seen in Table 1, the sample was complex in relation to comorbidity (86% had at least one other comorbid diagnosis), trauma history (e.g., 77% had previous sexual victimisation), and levels of past psychiatric hospitalisation (approximately 30% of the sample).

CPT = cognitive processing therapy; TAU = treatment as usual; FU = follow-up.

FIGURE 1 Flow of participant progress throughout the trial.

Procedures

Design

A randomised, repeated measures design was adopted with posttreatment assessments conducted 1 week following the completion of the CPT protocol and equivalent time period for TAU. Follow-up assessments took place at 3-, 6-, and 12-month follow-up. Participants were screened for suitability on contacting the service (either by phone or face to face). Those meeting basic inclusion criteria (e.g., sexual assault within past 4 weeks) undertook a clinical assessment following informed written consent. Following confirmation of eligibility, participants were sequentially randomised (1:1 ratio) to treatment by the project director. The project director generated the randomisation and allocated participants to groups. Participants were aware of the condition they were allocated to. Assessors did not provide therapy and were unaware at posttreatment and follow-up of treatment condition or degree of treatment received. Assessors did not report any failure of masking procedures. Participants received $50 for each posttreatment and follow-up interview.

Measures

ASD and PTSD diagnosis and symptom severity were the primary measures and assessed with the Clinician-Administered PTSD scale (CAPS; Blake et al., Reference Blake, Weathers, Nagy, Kaloupek, Gusman, Charney and Keane1995). The CAPS is a structured clinical interview that assesses the 17 symptoms of PTSD described in the DSM-IV PTSD criteria, and has additional symptom questions that can be used to derive ASD diagnosis. The 1(intensity)/2(frequency) rule for symptom presence was adopted (Weathers, Ruscio, & Keane, Reference Weathers, Ruscio and Keane1999). The intensity and frequency of each symptom can be rated on a 5-point scale and summed, resulting in an overall severity score. ASD criteria consists of 19 symptoms, but PTSD only 17 symptoms. Thus, we report CAPS severity scores and diagnosis for PTSD to be able to meaningfully compare outcomes across all assessmentsFootnote ⁴ (and were indexed to the recent trauma for which the client presented for treatment). Interrater reliability of diagnosis on a random sample of interviews (n = 20) was high (χ = 1.00; r [total severity score] = .80). Established measures were used to index self-reported PTSD symptoms and unhelpful trauma-related beliefs; the Posttraumatic Stress Disorder Checklist (PCL-S; Weathers, Litz, Herman, Huska, & Keane, Reference Weathers, Litz, Herman, Huska and Keane1993), and the Posttraumatic Cognitions Inventory (PTCI; Foa, Ehlers, Clark, Tolin, & Orsillo, Reference Foa, Ehlers, Clark, Tolin and Orsillo1999).

Secondary measures were current comorbid mood, other anxiety and substance use disorders and were assessed by the MINI International Neuropsychiatric Interview (MINI; Sheehan, Lecrubier et al., 1997). Interrater reliability for any current diagnosis (15 interviews) was high (χ = 1.00), with percentage agreement good for each category (mood: 100%, χ = 1.00; anxiety: 87%, χ = 0.71; substance: 87%, χ = 0.58). The Beck Depression Inventory (BDI-II; Beck, Steer, & Brown, Reference Beck, Steer and Brown1996) was also completed by participants. A structured clinical interview was used to document relevant information such as demographics, trauma history, medication usage, and so forth. In Session 1, clients completed the Credibility and Expectancy Questionnaire (CEQ; Devilly & Borkovec, Reference Devilly and Borkovec2000) to assess expectations regarding treatment success. Therapeutic relationship was assessed with the Working Alliance Inventory short form (WAI-S; Tracey & Kakotovic, Reference Tracey and Kokotovic1989). Clients and therapists completed the WAI at Sessions 2, 4, and 6.

Therapists and training

Nine female therapists who were regular staff members of Yarrow Place conducted therapy and were randomised to either CPT or TAU, with both groups being comparable in years of clinical experience working with sexual assault victims (CPT: M = 10.63, SD = 7.04; TAU: M = 12.38, SD = 5.15). All staff had a Bachelor of Social Work qualification, and two staff (one in each treatment condition) had Masters qualifications. None identified their therapeutic orientation as being specifically cognitive-behavioural. Therapists allocated to CPT received a 3-day workshop from R.D.V.N., followed by weekly group consultation of 1 hr initially, then approximately 30 min in the latter stages of the trial. TAU therapists received a briefing regarding the trial but no study-specific training or consultation.

Treatment conditions

CPT is normally delivered over 12 sessions (see Resick, Monson, & Chard, Reference Resick, Monson and Chard2007); however, a modified and abbreviated 6-session format that has previously been trialled (Nixon, Reference Nixon2012) was used. This 6-session manualised format adopted the framework and materials of the CPT manual (Resick et al., Reference Resick, Monson and Chard2007) and sessions (90-min duration) were scheduled weekly (the 90-min sessions ensured adequate coverage of CPT content, thus no components were omitted). Initial sessions introduced cognitive restructuring techniques, with later sessions introducing more advanced worksheets and with clients being introduced to alternative ways of thinking. The task of writing an account of the traumatic event for homework was done in Session 2. The processing of this event continued throughout treatment.

TAU encompassed a range of methods including psycho-education, supportive counselling, problem solving, interpersonal therapy, elements of mindfulness, acceptance and value-based techniques, and discussion of thoughts and feelings. Although on occasions elements of cognitive-behavioural techniques were apparent (e.g., discussion of in-vivo exposure to a feared situation such as going to a bar), this was not part of a systematic plan of graded exposure. Unhelpful beliefs were not specifically challenged in a structured fashion or through Socratic dialogue. On occasions, homework exercises were set (e.g., a values-oriented based exercise), but this was not routine. TAU sessions were scheduled according to the normal service delivery model and, as reported in the Results, TAU received a similar number of sessions as CPT in the active treatment phase of the trial, but over the course of the study TAU received more therapy.

Treatment fidelity

Therapy was audiotaped in both conditions. As detailed in the Supplementary Materials, CPT therapists’ adherence to essential CPT components and their competency was good. CPT and TAU therapists were rated on important therapeutic factors (i.e., genuineness, warmth, accurate empathy, professional manner) using the same scale. Mean ratings fell in the very good to excellent range, and effect sizes tended to favour CPT (ds ranging from 0 to 0.64).

Statistical Approach

Analyses were conducted with the intent-to-treat sample (ITT). These analyses reflected the context of the trial, an effectiveness versus efficacy study, and the fact that individuals vary in relation to the amount of treatment needed. For example, although originally designed as a 12-session protocol, not all PTSD clients need exactly 12 CPT sessions to reach good outcomes (Galovski, Blain, Mott, Elwood, & Houle, Reference Galovski, Blain, Mott, Elwood and Houle2012).Footnote ⁵ Full details on our statistical approach and justification are given in the Supplementary Materials. Given substantial attrition across posttreatment and follow-up assessments (50%, on average), multiple imputation was adopted for missing data using fully conditional specification, otherwise known as multivariate imputation by chained equations (MICE; van Buuren & Groothuis-Oudshoorn, Reference van Buuren and Groothuis-Oudshoorn2011; computed in R, a statistical computing environment; R Development Core Team, 2011). Simulations indicate that even with small samples and substantial missing data (e.g., sample N = 50, 80% missing data), multiple imputation such as MICE demonstrates good performance for addressing missing data (Schafer & Graham, Reference Schafer and Graham2002). The imputation model included all baseline symptom measures, treatment group, and outcomes (42 variables in total) to predict missing data. Typically, 15–25 predictor variables are usually sufficient to adequately account for missing data (van Buuren & Groothuis-Oudshoorn, Reference van Buuren and Groothuis-Oudshoorn2011); however, we used all the variables of interest to ensure adequate coverage. Relations between and within time were preserved and imputation values were constrained to the range of observed values in non-missing data.

In terms of sample size, previous intervention studies of ASD have observed large effects between trauma-focused CBT programs and supportive counselling conditions (e.g., Bryant et al., Reference Bryant, Harvey, Dang, Sackville and Basten1998; Bryant et al., Reference Bryant, Moulds and Nixon2003). An a priori power analysis indicated that a total sample of 60 would result in the ability to detect a moderate-to-large directional effect between treatment conditions (d = 0.65, power = .80, using G*Power 3.1.7; Faul, Erdfelder, Buchner, & Lang, Reference Faul, Erdfelder, Buchner and Lang2009). Accordingly, this was the targeted sample size.

Because we were unable to reach the planned sample size, we adopted an analysis and interpretative approach that focused on effect sizes and the confidence intervals around these effects (see Cumming, Reference Cumming2008, Reference Cumming2014; Faulkner, Fidler, & Cumming, Reference Faulkner, Fidler and Cumming2008, for detailed discussion of the superiority of effect sizes and confidence intervals vs. planned null hypothesis significance testing). For consistency with earlier research, we also report relevant inferential statistics. We analysed continuous measures (CAPS severity scores, PCL, BDI-II, PTCI) in a series of 2 × 2 mixed ANOVAs to generate required effect sizes and confidence intervals, and pooled the results across imputed data sets using Raghunathan and Dong's (Reference Raghunathan and Dong2013) formulae.

Categorical outcomes (PTSD status, response to treatment, good end-state function) were analysed by fitting a generalised linear model with binomial distribution and logit link function (i.e., a logistic regression) and pooled using MICE. Response to treatment was defined by a change of more than 12 points on the CAPS and total score below 45, with good end-state functioning (i.e., remission) defined by a total CAPS score below 20 (Monson et al., Reference Monson, Schnurr, Resick, Friedman, Young-Xu and Stevens2006; Schnurr et al., Reference Schnurr, Friedman, Engel, Foa, Shea, Chow and Bernardy2007). Numbers needed to treat (NNT) were calculated from good end-state functioning percentages. To reiterate, while inferential statistics (including p values) are reported, interpretations were based on magnitude of effects and their confidence intervals.

Results

In relation to preliminary analyses, there were generally clinically negligible differences between groups on relevant baseline variables, and between those who did and did not participate in follow-ups. Participants in both groups attended the same number of sessions in the pre- to posttreatment phase (3.5 sessions on average); however, TAU participants continued to have significantly more sessions between posttreatment and 12-month follow-up (with these clients having 4–5 additional sessions on average in each follow-up period). Treatment credibility and working alliance was comparable between groups (see Supplementary Materials for full details).

We conducted repeated measures ANOVAs on imputed data to examine changes on the primary measures of PTSD symptom severity and unhelpful beliefs (CAPS, PCL, PTCI), as well as the secondary outcome of interest, depression (BDI-II). Imputed descriptive statistics are presented in Table 2, pooled effect sizes in Table 3, and pooled inferential statistics are available in the Supplementary Materials (Table S1). In terms of PTSD, as expected, treatment resulted in large and clinically meaningful reductions for both groups at each follow-up relative to pretreatment. Examination of effect sizes showed these reductions ranged between 1.01 to 1.45 (CAPS), and 0.76 to 1.25 (PCL). Similarly moderate-to-large changes were seen for unhelpful cognitions (PTCI, d ranging from 0.42 to 0.94). Depression symptoms also reduced for both groups, with large effects seen across all follow-ups (ds between 0.42 and 0.92). It should be noted that a likely result of modest sample size and variability in scores resulted in rather large confidence intervals.

TABLE 2 CPT and TAU Imputed Means, Standard Deviations Over Time on All Measures (N = 46)

Note: CPT = cognitive processing therapy (n = 24); TAU = treatment as usual (n = 22); CAPS = Clinician-Administered PTSD scale; PCL = Posttraumatic Stress Disorder Check List; PTCI = Posttraumatic Cognitions Inventory; BDI-II = Beck Depression Inventory — 2nd Edition.

TABLE 3 Within- and Between-Group Pooled Effect Sizes (Cohen's d and 95% Confidence Intervals) From Pre- to 1-Year Follow-Up on All Symptom Measures (N = 46)

Note: CPT = cognitive processing therapy (n = 24); TAU = treatment as usual (n = 22); CAPS = Clinician-Administered PTSD scale; PCL = Posttraumatic Stress Disorder Check List; PTCI = Posttraumatic Cognitions Inventory; BDI-II = Beck Depression Inventory — 2nd Edition.

^a Positive values reflect CPT scores are lower than TAU scores.

In terms of between-group differences, we did not obtain clear evidence that the groups differed meaningfully due to the large confidence intervals observed. That said, and although there was some variability in the magnitude of effects between CPT and TAU, overall there was a reasonably consistent pattern of effects favouring CPT (see Table 3). Summarising these results, there was a small-to-moderate difference on the CAPS at pretreatment between the two groups (d = 0.39), with this difference remaining stable over the course of follow-ups (ranging between 0.31 – 0.50), indicating this baseline difference was maintained throughout. Self-reported PTSD (PCL) differences between groups that were negligibly different at pretreatment fluctuated across the follow-ups, slightly favouring CPT, but with effects being small in general (ds between 0.13 and 0.32). Clients’ unhelpful cognitions (PTCI) also showed fluctuation, with minimal difference between CPT and TAU seen at two assessments (3-month follow-up, d = 0.06; 6-month follow-up, d = 0.03), and moderate-sized differences in CPT's favour at posttreatment (d = 0.36) and 1-year follow-up (d = 0.66). In relation to depression, the degree of difference between the two groups, again favouring CPT, increased over the year after treatment (e.g., posttreatment, d = 0.13; 1-year follow-up, d = 0.41).

There were no significant adverse events in either condition. Based on available (non-imputed) data, and using a change of more than 12 points on the CAPS as an indicator of reliable change (Monson et al., Reference Monson, Schnurr, Resick, Friedman, Young-Xu and Stevens2006), two participants in CPT demonstrated worsening of symptoms at different periods. One participant was worse at posttreatment and 3-month follow-up (relative to her pretreatment score), and another participant at 12-month follow-up. Two TAU participants had an increase of exactly 12 points on the CAPS at 6-month follow-up. Interestingly, for these four participants, worsening of symptoms was not seen on their PCL scores.

In terms of diagnostic outcomes, the pooled results demonstrated increasingly smaller differences between the groups in PTSD diagnostic status across follow-ups. At posttreatment, 36% and 57% of the CPT and TAU groups were diagnosed with PTSD (CAPS), odds ratio (OR) = 0.41, 95% CI [0.07, 2.32], p = .29. At the 3-month follow-up, 49% (CPT) and 58% (TAU) had PTSD, OR = 0.69, 95% CI [0.09, 5.21], p = .70. By the 6- and 12- month follow-ups, these differences were negligible (6 months: 50% CPT, 46% TAU, OR = 1.20, 95% CI [0.15, 9.27], p = .85; 12 months: 51% CPT, 46% TAU, OR = 1.24, 95% CI [0.21, 7.33], p = .80).

The proportion of participants showing a response to treatment (i.e., a change of more than 12 points on the CAPS resulting in a total score below 45) was similar. There was little difference between the groups at posttreatment, with 73% and 69% of the CPT and TAU groups showing response (OR = 0.86, 95% CI [0.14, 5.17], p = .86). Remaining follow-ups showed a similar pattern, with a slightly larger difference at 3-months’ follow-up: at 3 months, 55% of CPT versus 36% of TAU participants showed a response, OR = 2.19, 95% CI [0.89, 14.75], p = .39; at 6 months, 50% CPT versus 51% TAU, OR = 1.05 (95% CI [0.18, 6.11], p = .95; and at 12 months, 60% CPT versus 50% TAU, OR = 1.52 (95% CI [0.23, 9.94], p = .64.

In terms of good end-state functioning, effects in the small–moderate range favoured CPT. Thus, at posttreatment, 45% of CPT participants versus 31% of TAU met good end-state criteria (OR = 1.82, 95% CI [0.30, 10.96], p = .49), and at the 3-month follow-up, 33% CPT versus 12% of TAU participants.Footnote ⁶ At 6 months, this difference was less pronounced (35% CPT, 27% TAU, OR = 1.50, 95% CI [0.26, 8.48], p = .63), but became slightly larger by the 12-month follow-up, with 50% of CPT participants meeting good end-state functioning versus 31% of TAU, OR = 2.30, 95% CI [0.41, 12.97], p = .32.

In terms of numbers needed to treat (NNT) to reach good end-state functioning, these ranged from 3.08 to 11.65, depending on the time of assessment. NNT was 6.73 on average, indicating that the added benefit of using CPT relative TAU (in terms of an additional participant meeting good end-state functioning) would be seen for every seven individuals treated with CPT.

Additional analyses

A large number of potential predictors of posttreatment and 12-month outcome were available. As detailed in the Supplementary Materials, after controlling for group and pretreatment severity, no demographic or trauma characteristic variables accounted for PTSD outcomes.