Development and validation of the BD S_X: a brief measure of mood and symptom variability for use with adults with bipolar disorder

Objectives: Ecological momentary sampling in BD research requires brief symptom measures with low cognitive demands to maximize data collection across the range of BD symptomatology. We developed the BD S_x cognizant of the challenges inherent in scale development with low prevalence populations and the limitations of existing measures (e.g., over-reliance on patients in acute states recruited from psychiatric settings). In order to be generalizable across the full spectrum of the illness, we also included those currently euthymic and those who avoid clinical contact. Methods: We recruited a global sample of 1010 adults with BD over 19 days using socio-demographically targeted, social media advertising and online data collection. At follow-up, 428 participants provided responses 67 days later on average. This enabled us to develop the BD S_x and replicate initial findings across multiple samples over time. Results: Both exploratory and confirmatory factor analyses support a 4-factor BD S_x model. Goodness of fit indices indicate good model fit across samples and over time. We labeled these factors: elation/loss of insight, affrontive symptoms of mania, cognitive/depressive, and somatic/depressive symptoms. Affrontive symptoms correlate positively with cognitive and somatic depression factors, which may suggest mixed-state symptom clusters in accord with DSM 5. Conclusions: Responses to the BD S_x reliably measure both depressive and hypo/manic symptoms. Temporal invariance analyses indicate that the 4-factor structure is consistent over time. Future research  should compare BD S_x responses to clinical diagnoses of hypo/mania and major depressive episodes.