Kreft (1996) suggested 30 Level 2 groups and 30 Level 1 observations per group. Simulation studies indicate that the balance swings toward more than 30 groups and fewer than 30 observations per group for hypotheses about the effects of Level 2 variables (e.g., Maas & Hox, 2005; Snijders & Bosker, 1993). For a two-level model, Hox (2010) recommends at least 20 observations for 50 groups to test cross-level interactions, and at least 10 observations for 100 groups to test random effects.