33 Conceptualization and Measurement of Proactive Vitality Management among the items on the between-level (Jöreskog, 1999). Item-level ICCs (i.e., the amount of variance that can be attributed to the person-level) ranged from .52 to .67, indicating that a considerable amount of variance remained to be explained on the within-person level. Cronbach’s alpha coefficient of the daily proactive vitality management scale ranged from α = .95 to α = .97 over the five days. These results show that proactive vitality management can be adequately and reliably measured with the proposed eightitem instrument on a daily level. FIGURE 1 Results of the multilevel confirmatory factor analysis (MLCFA) on the eight daily PVM items. All reported values are standardized. Work-Related Strategies and Micro-Breaks at Work To examine how the use of work-related strategies and micro-breaks (Fritz et al., 2011; Zacher et al., 2014) relates to PVM, we measured these constructs over the course of five working days. Following the methodological strategy of Zacher et al. (2014), for each day 2
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