Outlier-response pattern checks to improve measurement with the Montgomery-Asberg depression rating scale (MADRS)

Symptom manifestations in affective disorders can be subtle. Small imprecisions in measurement can lead to incorrect estimation of change. Previously, expert-derived scoring inconsistency flags were developed for MADRS. Currently, we derive empirically based outlier-pattern flags, to further detect imprecisions in ratings. NEWMEDS data repository of almost 25,000 MADRS administrations from 11 registration trials of antidepressants was used to identify outlier response patterns reflecting potentially careless responses. Coverage of these flags was compared to previously published expert derived flags. Both sets of flags were also further tested in Monte Carlo simulated data as a proxy to applying flags under conditions of known inconsistency. The outlier flags derived provide cutting points to identify: (1) under and overuse of values (e.g., Scoring “1″ on 6 or more items), (2) disproportionate use of even or odd response choices (e.g., 8 or more odd values), (3) longest consecutive use of value (e.g., more than 5 items in a row scored with same value), (4) high variability within administration (standard deviation greater than 1.8), (5) outlier responses on multiple items (i.e., multivariate outliers), and (6) outlier scoring (e.g., scoring 4,5 or 6 on item 1). Outlier response flags were raised in 26% of the MADRS administration and in 97% of the Monte Carlo data. Of administrations with no expert flag, 21.7% had an outlier flag and of administrations with at least one expert flag, 27.7% also had an outlier flag. Outlier-pattern flags appear to be a useful adjunct to expert derived flags in the quest to improve measurement in clinical trials.