The repeated measurement of moods in everyday life, as is common in ambulatory monitoring, requires parsimonious scales, which may challenge the reliability of the measures. The current paper evaluates the factor structure, the reliability, and the sensitivity to change of a six-item mood scale designed for momentary assessment in daily life. We analyzed data from 187 participants who reported their current mood four times per day during seven consecutive days using a multilevel approach. The results suggest that the proposed three factors Calmness, Valence, and Energetic arousal are appropriate to assess fluctuations within persons over time. However, calmness and valence are not distinguishable at the between-person level. Furthermore, the analyses showed that two-item scales provide measures that are reliable at the different levels and highly sensitive to change.

The repeated measurement of moods and emotions with high frequency is common in ambulatory psychological and psychophysiological assessment. Measurement schedules range from one assessment per day taken for several weeks (e.g., Cranford, Shrout, Iida, Rafaeli, Yip, & Bolger, 2006) to high-frequency assessment within a 24 h period (e.g., Ebner-Priemer & Sawitzki, 2007; Myrtek, 2004). Because of the high repetition rate in such studies, the duration of a single assessment should be kept short to minimize the burden on participants. The higher the participants' burden caused by the frequency and duration of single assessments, the more likely their compliance and motivation to give valid responses will decline. Moreover, when participants need to rate redundant items, additional effects like the exaggeration of subtle differences between items may occur, compromising the psychometric properties of a scale (Bolger, Davis, & Rafaeli,2003; Fahrenberg, Leonhart, & Foerster, 2002; Lucas & Baird, 2006).

Consequently, some researchers have used single items to assess different facets of mood (e.g., Fahrenberg, Hüttner, &...