61 Proactive Vitality Management and Creative Work Performance with creative solutions to problems” (1 = totally disagree, 5 = totally agree). Cronbach’s alpha ranged from .86 to .90 over the three weeks. Control Variables Proactive personality, creative requirement, and job autonomy were included into the study and the analysis as controls because of their potential influence on proactive vitality management and creative work performance. Proactive personality and job autonomy may affect people’s tendency or opportunity to proactively engage in vitality management. In addition, both control variables have been linked to creativity in earlier studies (e.g., Kim, Hon, Crant, 20009; Oldham & Cummings, 1996). Moreover, creative requirement is seen as an important determinant of employee creativity (Unsworth et al., 2005), and may thus directly influence our hypothesized effects as well. Creative requirement was measured by asking participants to what extent they are evaluated on creativity in their work (i.e., suggesting that creativity is expected or even required). Response options ranged from 1 (not at all) to 5 (to a very high degree). A sixitem version of the Proactive Personality Scale (PPS; Bateman & Crant, 1993), validated by Claes, Beheydt and Lemmens (2005) was used to measure proactive personality. An example item is “I excel at identifying opportunities” (1 = totally disagree, 5 = totally agree). Cronbach’s alpha was α = .81. We measured job autonomy on a weekly basis using three items developed by Bakker, Demerouti, and Verbeke (2004), based on Karasek’s (1985) job content instrument. An example item is “Last week, I could decide myself how to execute my work” (1 = totally disagree, 5 = totally agree). Cronbach’s alpha ranged from .77 to .88 over the three weeks. Strategy of Analysis The data in the current study comprised a multilevel structure with weeks nested within persons. Therefore, we conducted multilevel analysis with the HLM 7.01 software (Raudenbush, Bryk, & Congdon, 2013) to test our hypotheses. Prior to testing our hypotheses we calculated the intra-class correlations (ICC) for both week-level variables, which shows howmuch of the variance can be attributed to the person-level. In line with our expectations, 42% of the variance in proactive vitality management could be attributed to the between-person level and a comparable amount (46% of the variance) was found for creative work performance. These findings indicate that a considerable amount of variance in these variables remained to be explained by the 3
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