Consistent with previous findings, various diagnostic and clinical severity variables at baseline emerged as being predictive of short term and long term clinical improvement. More specifically, the presence of comorbid social phobia and PTSD was associated with less clinical improvement at both 3 and 12 months. Both social phobia and PTSD have a chronic and unremitting course (Bruce et al., 2005
; Davidson et al., 2004
; Yonkers et al., 2003
) and it is likely that additive presence of these disorder specific symptoms, (e.g., social avoidance, concerns about embarrassment, and heightened physiological arousal) exacerbate the course of panic related symptoms. Similarly, greater severity of panic related symptoms, and phobic avoidance (including agoraphobic severity and overall fears) predicted poorer improvement at both time points. Greater disability at baseline, or impaired functioning in daily life, was also a stable predictor of poorer clinical improvement. As suggested by previous studies, anxiety disorders are often associated with work disability and impairment in daily routine activities (Carerra et al., 2006
; Sareen et al., 2006
; Stein et al., 2005
). The other variable that was associated with greater clinical improvement at both time points was having a college education. Education may be a proxy for income however it may also be a proxy for access, more access to information about anxiety related symptoms as well as access to resources. Demographic variables such as being female, age, and marital status were not significant at either time point. Lastly, attitudinal characteristics which included patient beliefs about psychotherapy and patient beliefs about medication were not significant at either 3 or 12 month time points.
In the final models predicting clinical improvement, few variables remained significant. As expected, intervention status was significant in all models, and consistent with previous studies and current bivariate findings, severity of symptoms and personality traits were the most important predictors of clinical improvement in this randomized effectiveness trial for panic disorder in primary care. More specifically, a higher level of anxiety sensitivity at baseline was related to a less favorable outcome at both 3 month and 12 month end points. Anxiety sensitivity (AS) has been defined as an excessive fear of anxiety-related sensations, and beliefs that these sensations are harmful (Reiss et al., 1986
; Reiss et al., 1991). In other studies, measures of anxiety sensitivity (i.e., the ASI) have been useful in prospectively identifying individuals who may develop panic attacks as well as those who many have persistent panic attacks in longitudinal studies (Li and Zinbarg, 2007
; Schmidt et al., 2006
). The severity score on the Fear Questionnaire is an overall index of phobic avoidance (which included avoidance related to agoraphobia, social phobia, and other specific phobic situations) and consistent with previous studies (Slaap and den Boer, 2001
) greater overall severity was also predictive of less clinical improvement at longer term follow-up in this study.
The personality domain, neuroticism, also was found to be a predictor of clinical improvement at 3 months; that is, lower neuroticism scores at baseline were related to clinical improvement. Neuroticism, a core factor in many personality models, has been defined as a predisposition toward negative affective states such as depression, anxiety, anger, and shame (Costa and McCrae, 1985
). In both clinical and general population studies alike, neuroticism has been identified as a risk factor for Axis I and Axis II disorders (Hettema et al., 2004
; Jylha and Isometsa, 2006
; Miller and Pilkonis, 2006
). In a recent study, neuroticism was significantly correlated with four of the 10 personality disorders (paranoid, borderline, avoidant and dependent personality disorder) and it was prospectively (12 months after initial intake) shown to be a predictor of depression and anxiety scores, occupational impairment and lower overall functioning (Miller and Pilkonis, 2006
). In general, personality styles involving avoidance and overdependence on others may seriously curtail clinical improvement as well as constrain the efficacy of various behavioral exposure tasks.
Lastly, being Caucasian (versus not being Caucasian) was associated with a more favorable clinical outcome at long-term follow-up (i.e., at 12 months). There are several possible explanations for this finding. In general, differential patterns of service utilization and treatment adherence may lead to disparities in quality of care and mental health outcomes (Alvidrez, 1999
; Schraufnagel et al., 2006
). Such patterns may be influenced by unfavorable attitudes and expectations about mental health treatment among ethnic minorities (Alvidrez, 1999
). In the current sample, ethnic minorities reported less favorable attitudes toward both medication and psychotherapy (Hazlett-Stevens et al., 2002
); however for the total sample (including Caucasians) patient beliefs were not associated with clinical improvement. Other variables which may differentially influence clinical outcomes include difficulties with language (Sleath et al., 2003
), logistic barriers (Barron et al., 2004
; Alvidrez and Azocar, 1999
), beliefs about causes (Barron et al., 2004
), stigma associated with mental health treatment (Alvidrez, 1999
; Barron et al., 2004
; Alvidrez and Azocar, 1999
) and the potential influence of social networks (Wynaden et al., 2005
In the final logistic regression models, demographic variables such as marital status, age, and gender were not predictors of clinical improvement at either time point. Also, attitudinal variables, (i.e., attitudes and beliefs about medication and psychotherapy) were not associated with clinical outcome which is somewhat inconsistent with a previous study including attitudinal variables (Clark et al., 1999
). Important to note, previous findings from the CCAP project (Hazlett-Stevens et al., 2002
) support differences in attitudes across ethnic groups, therefore attitudes may have a greater influence on clinical improvement in samples with greater ethnic minority representation. While bivariate relationships existed for other variables such as specific DSM-IV diagnoses (social phobia, agoraphobia, PTSD), as well as indices of health functioning and disability, these relationships were no longer significant in the presence of other clinical variables (i.e., anxiety sensitivity, fear severity and neuroticism).
This study has a number of limitations. First of all, treatment was delivered in university-affiliated clinics on the West coast which limits the generalizability of the findings. Second, while our list of potential predictors was rather comprehensive, some important possible predictors such as Axis II personality disorders were not formally assessed. Third, assessments were conducted by telephone rather than in-person which may have affected the psychometric properties of the interview and self-report assessments. Fourth, the majority of the patients were Caucasians and small sample sizes of each respective ethnic group did not allow for comparisons extending beyond Caucasian versus non-Caucasian categories.