The indicators in this report are based on information drawn from a variety of independent data sources, including national surveys of students, teachers, and principals, and data collections from federal departments and agencies, including the Bureau of Justice Statistics, the National Center for Education Statistics, the Federal Bureau of Investigation, and the Centers for Disease Control and Prevention. Each data source has an independent sample design, data collection method, and questionnaire design or is the result of a universe data collection. Universe data collections include a census of all known entities in a specific universe (e.g., all deaths occurring on school property). Readers should be cautious when comparing data from different sources. Differences in sampling procedures, populations, time periods, and question phrasing can all affect the comparability of results. For example, some questions from different surveys may appear the same, but were asked of different populations of students (e.g., students ages 12–18 or students in grades 9–12); in different years; about experiences that occurred within different periods of time (e.g., in the past 30 days or during the past 12 months); or at different locations (e.g., in school or anywhere).
All comparisons described in this report are statistically significant at the .05 level. The primary test procedure used in this report was Student's t statistic, which tests the difference between two sample estimates. The t test formula was not adjusted for multiple comparisons. Estimates displayed in the text, figures, and tables are rounded from original estimates, not from a series of rounding.
The following is a description of data sources, accuracy of estimates, and statistical procedures used in this report.