3.1 Descriptive statistics, demographics and clinical variables
Personality composite variables were examined to rule out the possibility that selection of individuals with DD’s truncated or skewed their distributions, which might increase the likelihood of Type II error. Both N and E composites were normally distributed and slightly restricted in range, relative to the full YEP sample (respectively: Kolmogorov-Smirnoff Z values of .77 and .57, both NS, and ranges of −1.55 to 2.37 and −2.53 to 1.67, akin to z-scores). Correlations are presented in .
Zero-order correlations and odds ratios for baseline predictors and follow-up clinical variables
Demographic variables (gender, race/ethnicity, SES) did not predict SI in separate Cox regression models (all χ2(1)≤1.52, NS). Similarly, clinical variables (baseline depression composite, baseline history of a clinically significant DD, baseline history of SI during a DD, whether the follow-up diagnosis was MDD or DD-NOS) did not predict SI (all χ2(1)≤2.35, NS).
3.2 Personality traits
In aggregate, baseline E inversely predicted SI in males only, while baseline composite N was not significantly related to SI for either gender. More specifically, gender and N scores were simultaneously entered in the first block and the N × Gender interaction was entered in the second block, with SI as the dependent variable. This model was not significant (). By contrast, when gender, E and their interaction were examined in the same fashion, the E × Gender interaction significantly predicted SI (). The data were examined separately by gender to decompose the interaction. E inversely predicted SI in males (χ2(1)=9.42, p<.01; b=−1.28, SE(b)=.46, HR=.28, 95% CI [0.11, 0.68]), but not in females (χ2(1)=0.00, NS, b=.002, SE(b)=.31, HR=1.002, 95% CI [0.55, 1.83]; ).
Results of select Cox regression models
Baseline extraversion score by gender and follow-up suicidal ideation (SI). Of the 117 participants studied, n = 22 females (24.4%) and n = 8 males (29.6%) endorsed SI during a follow-up DD.
To determine whether the effect was attributable to certain scales of the E composite, the three scales were entered in a model including males only. Results showed that the Big Five Mini Markers Extraversion scale inversely predicted SI, and the BAS Drive subscale approached significance as an inverse predictor (). To determine whether the effect of E on SI in males with DD’s could be accounted for by interpersonal problems, E and the four domains of interpersonal problems were entered simultaneously in a Cox regression model. E remained a significant predictor of risk (b=−2.79, SE(b)=1.41, p<.05, HR=.06, 95% CI [0.004, 0.98]).
3.3 Interpersonal problems
In aggregate, the results showed that interpersonal problems within one’s social circle predicted SI regardless of gender. More specifically, separate Cox regression models predicting SI during DD were examined for each interpersonal domain: best friend, social circle, romantic and family relationships. Models including gender demonstrated no significant main effects or interactions with gender (for blocks adding gender, χ2’s(1)≤1.38, NS, with the exception of Gender × Romantic Relationships, which approached significance, χ2(1)=2.81, p=.095). Thus, the analyses of interpersonal problems are reported without gender. Interpersonal problems in the social circle domain predicted SI (χ2(1)=4.09, p<.05 b=.40, SE(b)=.20, HR=1.49, 95% CI [1.01, 2.21]). No other interpersonal domains of the LSI predicted SI (all χ2(1)≤0.89, NS). When all four domains were entered in a model, social circle’s effect size was slightly larger than previously (HR=1.55) and approached significance (p=.064). Therefore, although including all domains reduced power, other domains of interpersonal problems did not account for the effects of the social circle domain.