As can be seen in , about 54% of study respondents were women. In addition, 13% of residents had a history of pre-disaster depression and 12% had a history of pre-disaster panic attacks. Over 10% met the DSM-IV criteria for a perievent panic attack, while 11% met criteria for year-1 depression and 12% met criteria for year-2 depression.
Bivariate Pearson's correlation coefficients among the observed variables in the SEM model were calculated (available upon request). Briefly, PEP was associated with all of the depression symptoms for both year-1 (rs ranging from .16 to .22, all ps<.001) and year-2 (rs ranging from .09 to .21, all ps <.001). PEP was also associated with WTCD exposure (r =.20, p < .001), year-2 negative life events (r =.16, p<.001), year-2 traumas (r =.09, p<.001), year-2 self-esteem (r = -.16, p<.001), and year-2 social support (r = -.10, p<.001). Finally, higher exposure to WTCD events was associated with all of the year-1 and year-2 depression items (all ps < .001), as well as year-2 negative life events (r =.16, p<.001), traumas (r =.09, p<.001), and self-esteem (r = -.08, p<.001), but not social support (r = -.01, p>.05).
Although these correlations are suggestive, due to confounding, the longer-term direct impact of PEP on mental health status cannot be inferred from these data. Therefore, we assessed the direct effects of PEP on year-1 and year-2 depression measured as latent constructs, controlling for other factors. As described, we initially allowed the error terms for each year-1 depression symptom to correlate with its year-2 counterpart. All of the exogenous variables (i.e., demographic and pre-disaster mental health measures) were allowed to correlate with each other. We also allowed all of these measures to have direct effects on all of the endogenous variables (e.g., income on exposure, PEP, stressor events, psychosocial resources, year-1 depression, and year-2 depression). The model specified direct effects between all year-1 endogenous and year-2 endogenous variables (e.g., PEP on year-2 stressor events, year-2 psychosocial resources, year-1 and -2 depression) and contained 4 observed exogenous variables, 26 observed endogenous variables, 4 unobserved endogenous variables, and 30 unobserved exogenous variables, for a total of 64 variables. The model also estimated 16 covariances and 34 variances. With 465 distinct sample moments and 108 parameter estimates, the model had a χ2 = 2229.94 (df = 357, p < .001). Other indices suggested that our model could be improved, with a root mean square error of approximation (RMSEA) = .056 (90% CI = .054 - .058), Bentler-Bonett normed fit index (NFI) = .921, and comparative fit index (CFI) = .933. To increase the model's parsimony and reduce the possibility that we over controlled with the pre-disaster panic mental health measure, we eliminated non-significant direct pathways for this measure. We eliminated correlations between the four exogenous variables (e.g., gender and income) that were not significant. Finally, we examined the modification indices and allowed error terms for several of the depression indicators to correlate. After these changes, we recalculated all parameter estimates. The new model contained 465 distinct sample moments, 107 parameter estimates, and a χ2 = 1402.23 (df = 358, p<.001). Based on the fit statistics, this second specified model adequately fit the data, with a RMSEA = .042 (90% CI = .039 - .044), NFI = .950, and CFI = .962.
presents a simplified depiction of the final structural model with standardized coefficients, indicating significant direct paths, and omitting correlated error terms. (A complete final SEM model is available from the corresponding author.) As can be seen in and , World Trade Center Disaster exposure increases the likelihood of a PEP, year-1 depression, and year-2 stressor events (β = .22, p < .001). PEP is directly related to year-1 depression (β = .16, p < .001), but not to year-2 depression (e.g., β = .03, p = .189). It also increases year-2 stressor events (β = .14, p<.001) and lowers year-2 psychological resources (β = -.09, p = .007). Year-1 depression is positively related to greater year-2 stressor events (β = .24, p < .001), negatively related to year-2 psychological resources (β = -.17, p < .001), and positively related to year-2 depression (β = .14, p < .001). As expected, both year-2 stressor events and year-2 psychosocial resources are associated with year-2 depression (β = .38 and -.39, respectively, p < .001).
Simplified Depiction of Final Structural Equation Model for Perievent Panic and Major Depression (N=1681)*
Table 2 Structural Equation Model – Unstandardized Coefficients and Standardized Coefficients for Direct Effects Linking Demographic, Pre-WTCD Mental Health, WTCD Exposure, Perievent Panic, Stressful Events, Psychosocial Resources, and Depression (N=1,681) (more ...)
Further examination of variables in the model () shows that both income and pre-disaster depression were associated with greater exposure to the World Trade Center Disaster (p < .001). For PEP, income lowered the likelihood of this outcome (p < .001), while being female, having pre-disaster depression or panic, and greater exposure to the WTCD increased the likelihood of this psychological problem (p = .002, .006, .004, .001, respectively). Income and a history of depression were related to year-1 depression (ps < .001, for both associations), with income negatively related to this endogenous variable. Of the demographic or pre-disaster variables, only pre-WTCD depression was related to year-2 stressor events (β = .086, p=.013). Being female (β = .072, p=.025) and having a higher income (β = .428, p<.001) increased year-2 psychological resources, while pre-disaster depression decreased these resources (β = -.112, p = .001). Finally, none of the demographics or pre-disaster mental health measures was associated with year-2 depression.
Mediation is suggested when an independent variable has an association with a dependent variable and the association between them is significantly reduced after the mediated variable is included in the model. For this study, we only discuss the direct, indirect, and total effects of PEP on year-2 depression, as mediated by year-1 depression, year-2 stressor events, and year-2 psychological resources. The standardized total effect of PEP on year-2 depression is .19, which means that the indirect or mediated effect of this variable on year-2 depression is .16 (.19-.03 = .16). More specifically, individuals who meet criteria for PEP have about a .19 standard deviation increase in the probability of having depression two years after the WTCD. However, that increase is almost entirely due to the fact that those individuals who have a perievent panic attack are also more likely to suffer from year-1 depression, experience more stressor events between year-1 and year-2 post-disaster, and have fewer psychosocial resources two years post-disaster.