Educational researchers commonly use the rule of thumb of "design effect smaller than 2" as the justification of not accounting for the multilevel or clustered structure in their data. The rule, however, has not yet been systematically studied in previous research. In the present study, we generated data from three different models…

In some educational research studies--particularly longitudinal studies requiring a probability sample of schools and spanning a wide range of grades--it is desirable to so select the sample that schools at different levels (e.g., elementary and secondary) "correspond." This has often proved unachievable, using standard methods of selecting school…