Fig. 1.

A Design Appropriate for the “Site-level Longitudinal Effects of Population Health Interventions” (SLEPHI) Method Note. Different individuals are recruited at different time points from the same schools. Horizontal bars illustrate the same population health intervention implemented in 5 schools. For example, School 1 implemented the intervention in the year 2000. Vertical lines illustrate 3 student health surveys (in 2003, 2008, and 2013), in which all 5 schools participated. Within each survey, the intervention lengths vary across schools. For example, at Survey 2, the lengths of intervention in Schools 1–5 were 8, 5, 3, 0, and 0 years, respectively. As a rough guide, at least 50 sites (schools) are recommended to ensure statistical power (Maas & Hox, 2005). In addition, no more than 10 cycles of cross-sectional data (surveys) should be included (Asparouhov & Muthén, 2012a).