Social functioning

We employed three complementary measures of SF including self-reports (Provision of Social Relations Scale, PSRS) [40], informant reports (Specific Levels of Functioning Scale, SLOF) [41], and clinician-administered interviews (Scale for the Assessment of Negative Symptoms, SANS) [33]. The PSRS is a 15-item self-report scale measuring social relationships with family and friends. Items are scored on a 5-point scale (from 1 = “Very much like me” to 5 = “Not at all like me”) with higher scores indicating lower support and relationship quality. The PSRS was found to have alpha coefficients of 0.85, 0.80, and 0.78 among individuals with schizophrenia, bipolar disorder, and healthy controls, respectively [42], as well as solid test–retest reliability of 0.75–0.87 [43]. The SLOF is a 43-item scale assessing multiple domains of daily functioning. Items are rated on a 5-point Likert scale with total scores ranging from 43 to 215 and higher scores indicating better overall functioning. The SLOF was found to have alpha reliability of 0.62 [41]. An informant version of the SLOF was administered to caregivers of all study participants, typically first-degree relatives who were in regular contact with study participants. For data analyses, we used the total score of the SLOF’s Interpersonal Relations subscale. The SANS is a 25-item clinician-administered scale developed to measure negative symptoms in schizophrenia, which have been linked to SF [44]. Items are rated on a 6-point scale (range 0–5), with higher scores reflecting increased severity. For the purposes of assessing SF, we used an Asociality subscale item from the SANS, which indexes the ability to feel intimacy and closeness with others (item #20). The interrater reliability for this individual item of the SANS was found to be 0.90 [33].