This study examined potential predictors of treatment outcome in two evidence-based treatments for PTSD: CPT and PE. We hypothesized that several cognitive and affective variables would be related to both treatment dropout as well as treatment efficacy. Overall, results supported our hypothesis that cognitive variables would influence dropout; specifically, both lower intelligence and education were related to a greater likelihood of premature termination. However, in contrast with expectations, none of the cognitive variables demonstrated main effects on treatment efficacy. Further, comorbid affective states did not appear to affect treatment dropout, but depression and guilt appeared to impact treatment efficacy in an unexpected direction. There were two significant predictor by treatment condition interactions. Each of these are discussed below.
Consistent with several prior studies, but in contrast with our findings for the other cognitive variables, age was negatively related to dropout (Cloitre et al., 2004
; Foa et al., 2005
). Thus, it seems relevant for treatment providers to be aware that younger women may be more likely to end treatment prematurely and perhaps do more to strengthen their commitment to treatment at its onset. More research is needed to determine what it is about younger age that contributes to drop out. It may be that younger clients have more competing demands on their time or are more ambivalent about treatment than older clients. In turn, this may override any potential benefit of greater openness to changing beliefs and established patterns of thinking on this indicator of treatment outcome. Given that this finding has now been replicated, it will be important to turn efforts toward determining underlying causes. Another relevant direction for future work will involve replicating this finding in a male sample. The three studies that have addressed this research question have all been limited to female participants, and the results may not apply equally well to men.
In contrast with expectations for the treatment efficacy results, both depression and global guilt at pretreatment demonstrated main effects on treatment efficacy in an opposite direction than expected. Interestingly, although higher scores on each were related to higher initial PTSD symptomatology, individuals with higher depression and guilt demonstrated a greater relative reduction in PTSD over time, thus playing “catch up” with their counterparts with lower degrees of depression and guilt. This finding highlights the effectiveness of both treatments for individuals with more severe PTSD, as well as their effectiveness for individuals who have comorbid symptoms. Results do not appear to support the hypothesis that these affective states would interfere with successful processing of trauma memories or cognitive work.
No significant main effect on treatment efficacy was found for anger. Including the present study, there have now been three studies that have not found any effect of anger on treatment success (Cahill et al., 2003
; van Minnen et al., 2002
) and four studies (Foa et al., 1995
; Forbes et al., 2003
; Speckens et al. 2006
; Taylor et al., 2001
) that found that higher anger was associated with worse outcomes. One potential explanation for some of the contradictory findings is that both the Foa (Foa et al., 1995
) and Cahill (Cahill et al., 2003
) studies included a measure of state anger
at pretreatment which may vary as a result of situational factors. Because our goal was to assess characteristic levels of anger that are likely to be relevant across a variety of different situations, we used the measure of trait anger
for the current study. The van Minnen et al. (2002)
study used both state and trait measures of anger and Forbes et al. (2003)
used a measure of tendency to be angry toward other persons. Spreckens et al. (2006) asked about general anger and irritability over the previous month. On the other hand, Taylor et al. (2001)
used a measure of anger at others responsible for the car crash. Future studies will need to clarify and provide justification for the measurement of anger used, in light of the discrepancies in the field in assessing this affective condition.
One of the aims of the current study was to explore whether there were differential cognitive and affective predictors for the two treatment conditions. In terms of dropout, we found a significant interaction for anger and treatment condition suggesting that higher trait anger is more strongly related to dropout in PE compared to CPT. This result was evident despite the fact that, overall, completers did not differ from dropouts on levels of trait anger which suggests a unique relationship between PE, anger, and dropout. As described earlier, the current literature on client anger and PE is mixed, and most research has focused on treatment efficacy, not dropout rates. To our knowledge, only van Minnen and colleagues (2002)
examined the effects of pretreatment anger on dropout
in PE. In contrast to their null finding, we found that pretreatment trait anger, as measured by the STAXI, was associated with dropout. This result has implications for clinical work. If replicated, individuals who are high in trait anger may need to be identified prior to starting treatment and their commitment to PE may need to be strengthened to reduce the risk of premature termination. Alternatively, it’s possible that clients with high trait anger at pretreatment would be better served by an alternative treatment, such as CPT.
In terms of treatment efficacy, there was one significant interaction between age and treatment condition. It appears that younger age in CPT and older age in PE are related to the best outcomes, whereas older age in CPT and younger age in PE are related to relatively worse outcomes (though all groups demonstrate symptom reduction over time). It is possible that differences in the focus of the two different cognitive behavioral therapies account for this finding. More specifically, it may be that as people age, they have more difficulty changing long standing cognitions and instead benefit from greater trauma exposure and emotional processing or longer cognitive therapy with more repetitions. To some extent, this interpretation is consistent with the idea raised earlier that both the willingness and ability to learn new ways of thinking may be an important factor in understanding who benefits most from different cognitive behavioral treatments. This finding is intriguing and awaits replication and explanation.
The finding that age interacted with treatment condition to predict change over time underscores the importance of examining different treatments separately. That is, results for the entire sample demonstrated no effect of age on treatment efficacy. Investigating this relationship by treatment condition, however, yielded a potentially important finding that would have otherwise been missed. Because different treatments have different theories underlying their proposed mechanisms of change, it seems necessary to examine potential differences in associations based on treatment type.
With the exception of age, there were no differential predictors of efficacy for the two treatments that were examined in this study. We believe this underscores the robustness of both treatments in their effectiveness for treating PTSD within this population. The effectiveness of these treatments may have also contributed to the fact that there were few unique predictors of change over time. Because nearly all the participants were improving with treatment, this naturally cuts down on the amount of variability in PTSD scores over time. It is also important to note that although this study represents an advance over other studies with small sample sizes, the sample of sexual assault victims is still limited in its generalizability.
This study included only women in treatment for PTSD as a result of a rape and, therefore, results may not apply to other PTSD populations. In addition, future research would benefit from the inclusion of stronger measures of cognitive functioning than were available for this study. Although age, intelligence, and education served as useful indicators of openness to experience in this study, it will be important to include a more direct measure of this construct in future research. Of particular concern is the interpretation of the results related to age. While younger age has been found to be related to greater openness to new ways of thinking (Donnellan & Lucas, 2008
), effects for age are likely to be most robust in samples that include a greater proportion of older women than were included in this study. Furthermore, we did not have data for individuals after they dropped out of treatment. It is possible that some individuals could have dropped out of treatment because they experienced significant improvement with a shorter course of therapy (Monson et al., 2006
; Resick et al., 2002
; Resick et al. 2008
). Thus, dropout may not always be a sign of poor treatment outcome. However, given that half of the individuals who dropped out of treatment in both conditions completed less than one-third of the therapy sessions, it is unlikely that significant improvement preceded a great number of cases. Future studies should examine this issue more thoroughly.
Another point to mention is that individuals who dropped out of treatment were, by definition, omitted from analyses of predictors of treatment efficacy. This exclusion necessarily limits variability for the variables found to be significant for dropout (intelligence, education, and trait anger) for the efficacy analyses. Thus, the examination of the impact of intelligence, education, and anger on treatment efficacy likely excludes those with the lowest levels of intelligence and education and highest levels of trait anger. However, to the extent that these individuals are not willing to complete treatment, then the question of how their levels of intelligence, education, or anger would impact treatment efficacy might be considered somewhat premature. More research is needed to parse out the differential impact of these variables on dropout and treatment efficacy.
It is imperative that other studies replicate these findings. At this point, it is premature to say, for example, that younger women should be given CPT while older women should be given PE or that women with high trait anger should not be treated with PE. However, this study represents an important first step in its application of a sound theoretical framework to suggest hypotheses regarding which treatments work for whom, providing results that can highlight potential areas for improvement. This knowledge can be used to inform treatment decisions and ultimately produce better outcomes.