As several lines of evidence point to irregular biological rhythms in bipolar disorder, and its disruption may lead to new illness episodes, having an instrument that measures biological rhythms is critical. This report describes the validation of a new instrument, the Biological Rhythms Interview of Assessment in Neuropsychiatry (BRIAN), designed to assess biological rhythms in the clinical setting.

Eighty-one outpatients with a diagnosis of bipolar disorder and 79 control subjects matched for type of health service used, sex, age and educational level were consecutively recruited. After a pilot study, 18 items evaluating sleep, activities, social rhythm and eating pattern were probed for discriminant, content and construct validity, concurrent validity with the Pittsburgh Sleep Quality Index (PSQI), internal consistency and test-retest reliability.

A three-factor solution, termed sleep/ social rhythm factor, activity factor and feeding factor, provided the best theoretical and most parsimonious account of the data; items essentially loaded in factors as theoretically intended, with the exception of the sleep and social scales, which formed a single factor. Test-retest reliability and internal consistency were excellent. Highly significant differences between the two groups were found for the whole scale and for each BRIAN factor. Total BRIAN scores were highly correlated with the global PSQI score.

The BRIAN scale presents a consistent profile of validity and reliability. Its use may help clinicians to better assess their patients and researchers to improve the evaluation of the impact of novel therapies targeting biological rhythm pathways.