Capturing affective states in everyday life - Comparing psychometric properties of two affect measures.

E-diary items and scales face three contradicting challenges, originating from their repeated assessment: To achieve high compliance and to limit participant's burden a minimal number of items is aspired, to achieve reliability on a momentary level more items per scale are advantageous. As psychometric properties and distributions of e-diary scales are important but rarely reported, we used a clinical- (N = 51) and a community-based (N = 353) intensive longitudinal dataset comprising the momentary Multidimensional Mood Questionnaire (mMDMQ) and the Positive and Negative Affect Items (PNAI), both measuring affect, to investigate and compare, in an exploratory approach, distribution indices, psychometric properties, and assumptions for multilevel modeling. In the community sample, all scales of the mMDMQ and the positive affect scale of the PNAI showed very good psychometric properties and distributions. In contrast, the negative affect scale of the PNAI showed right-skewness and floor effects on the item and scale level, and even in the residuals of the multilevel models. In the clinical sample, the overall picture was opposite with mMDMQ again showing reasonable distributions, but this time positive affect of the PNAI revealing problematic properties. Carefully selecting momentary scales and reporting their psychometric properties is essential in e-diary research.