Assessing Mood in Daily Life Structural Validity, Sensitivity to Change, and Reliability of a Short-Scale to Measure Three Basic Dimensions of Mood Peter Wilhelm 1 and Dominik Schoebi 1,2 1 University of Fribourg, Switzerland, 2 University of California, Los Angeles, USA Abstract. 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. Keywords: ambulatory assessment, ecological momentary assessment, electronic diary, mood, affect, multilevel confirmatory factor analysis Introduction The repeated measurement of moods and emotions with high frequency is common in ambulatory psychological and psychophysiological assessment. Measurement sched- ules 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). Be- cause 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 assess- ments, the more likely their compliance and motivation to give valid responses will decline. Moreover, when partici- pants 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, Hütt- ner, & Leonhart, 2001; Myrtek, 2004). The use of single items, however, raises the problem that the reliability of the state specific component of the measure cannot be deter- mined and separated from measurement error. Therefore, a variety of multi-item mood scales have been used, ranging from long item lists (e.g., Buse & Pawlik, 1996; Kubiak & Jonas, 2007) to specifically designed or adapted short scales (e.g., Cranford et al., 2006). For these short scales, reliability coefficients and sometimes factor structures have been reported, which are usually based on the analy- ses of the between-person variance (e.g., individuals’ av- erages over time). Yet, the within-person variance has often been ignored (for exceptions see e.g., Buse & Pawlik, 1996, 2001; Cranford et al., 2006; Schimmack, 2003; Zelinski & Larsen, 2000; Zevon & Tellegen, 1982). The goal of this article is to evaluate the psychometric properties of a parsimonious six-item mood measure that was developed to assess three basic dimensions of mood in peoples’ daily lives. We do so using a multilevel modeling approach to investigate the variance and covariance be- tween items at the between-person and the within-person level simultaneously. What Are Moods? Moods are rather diffuse affective states that subtly affect our experience, cognitions, and behavior. They operate continuously and “provide the affective background, the emotional color to all that we do” (Davidson, 1994, p. 52). Moods can be consciously experienced as soon as they gain the focus of our attention, and are then characterized by the predominance of certain subjective feelings. Moods should be distinguished from emotions. Al- though the definition of emotions depends heavily on the- oretical frameworks (e.g., Ekman & Davidson, 1994; Lew- DOI 10.1027/1015-5759.23.4.258 European Journal of Psychological Assessment 2007; Vol. 23(4):258–267 © 2007 Hogrefe & Huber Publishers