This study examined the relationship between patient adherence to between-session EX/RP assignments and EX/RP outcome using a valid and reliable adherence measure in adults with OCD. As hypothesized, patient adherence significantly predicted post-treatment OCD severity. Moreover, the degree of patient adherence was significantly associated with the degree of improvement and the odds of response. In addition, early patient adherence and change in early patient adherence each significantly predicted post-treatment OCD severity. Patient adherence fully mediated the effects of other significant predictors on outcome.
Our findings are consistent with prior research (Abramowitz, et al., 2002
; De Araujo, et al., 1996
; de Haan, et al., 1997
; Tolin, et al., 2004
) and advance the literature in several important ways. First, unlike the prior studies, we used a patient adherence scale with demonstrated reliability and validity and measured patient adherence prospectively at each exposure session. Because dismantling studies found that exposures and ritual prevention are each key to good outcome (Foa, Steketee, Grayson, Turner, & Latimer, 1984
), the scale focuses on the quantity and quality of patient adherence to these essential EX/RP procedures. Such focus may be key to revealing the relationship between patient adherence and treatment outcome. Second, our data indicate that it is important for patients to achieve better than good homework adherence across all exposure sessions: only these patients are likely to achieve minimal symptoms. Third, we found that not only mean adherence but also early adherence (both mean early adherence and change in early adherence) affect treatment outcome. Finally, patient adherence fully mediated other predictors of outcome in this sample. If true in other samples, this may explain why OCD predictor studies often have found small or inconsistent effects on treatment outcome: study samples vary in patient characteristics, different patient characteristics can affect patient adherence, and patient adherence--although rarely measured--may be one of the strongest predictors of outcome and mediate other predictors’ effects.
These findings have clinical implications. Consistent with other studies (Maher, et al., 2010
), the data suggest that patients with severe OCD symptoms need not be excluded from EX/RP as practice guidelines suggest (American Psychiatric Association, 2007
). Instead, therapists should carefully monitor patient adherence with between-session assignments to ascertain who is likely to have a good response. If the link between patient adherence and treatment outcome is proven to be causal, then interventions that improve patient adherence should be provided to those with poor early adherence, and this should lead to better treatment outcome. Such therapeutic tailoring is consistent with a personalized care model.
The study has several limitations. The sample size and number of therapists was small, and the study was designed for other purposes. Thus, replication is warranted. We suspect that when EX/RP is delivered in a weekly format (as it is by most community providers), the effects of between-session patient adherence on OCD outcome might be even more robust. Second, like many studies of patient adherence, there is the potential confound between patient adherence and treatment outcome measures. Thus, we conducted sensitivity analyses, which yielded similar findings, and examined early adherence, where this confound is not present. Third, therapists rated patient adherence using patients’ self-report. A subset of sessions were reviewed by independent raters as part of another study, and reliability was excellent (Simpson, Maher, et al., 2010
). However, self-reports are subject to patient recall.
In summary, patient adherence to between-session EX/RP assignments significantly predicted treatment outcome, as did early patient adherence and change in early adherence. Patient adherence mediated the effects of other predictors of outcome. Future studies should establish that the link between patient adherence and treatment outcome is causal and develop interventions to improve adherence. These interventions could then be used to personalize care.