Measurement equivalence of the BDS scale with young and older adults with bipolar disorder.

Instruments developed for mental health research are commonly devised and validated with young adults only. However, the measurement properties of these scales may differ over the lifespan. For this study, we set out to demonstrate the psychometric equivalence of the BDSx scale with an international sample of young and older adults with bipolar disorder (BD). We independently replicated the 4-factor model of BDSx responses with young and older participants (M = 45.63, range 19-87 years of age); we then compared the psychometric properties between models. This allowed us to compare responses to each BDSx item between groups, and the strength of association among depression and hypo/mania factors (cognitive depressive symptoms, somatic depressive symptoms, affrontive symptoms of hypo/mania, elation/loss of insight). Young and older adults responded to 19 of 20 BDSx items in similar ways. Only responses to the 'talkative' item were significantly higher for younger adults. Correlations between depression and mania factors are statistically indistinguishable between age groups. This suggests that symptoms cluster and present similarly for young and older adults with BD. The BDSx is currently being used for ecological momentary sampling of mood by the BADAS (Bipolar Affective Disorder and older Adults) Study app for iPhone.