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Prevalence of Substance Use Among Racial & Ethnic Subgroups in the U.S.

2.4 Statistical Methods

Percentage estimates in the text tables of Chapters 3-5 have been rounded to the nearest one-tenth of one percent and screened to determine whether they meet a required level of statistical precision. Differences between racial/ethnic categories and other demographic subgroups that are reported in the text are statistically significant at the .05 level.

Appendix A discusses details of the statistical precision requirements, sample weighting, and statistical estimation and testing techniques. The tables of Appendix A present standard errors for all statistical estimates that are presented in the text of this report. Like the estimates themselves, the standard errors fully take into account the complex sample design of the NHSDA.

In interpreting the statistical estimates of this report, it is useful to remember that associations between variables are more likely to be statistically significant when the sample size is large. Thus, if differences in substance use prevalence by racial/ethnicity are found to be significant in the total population aged 12 and older but not significant within either the 12 to 17 or the 18 and older age groups, this does not mean that there are no real differences by race/ethnicity within age groups. It only means that such differences cannot be inferred given samples of the size used in this report. In general, associations involving substance use or dependence measures with low overall prevalence are more difficult to identify as statistically significant than associations involving measures with high overall prevalence.

Although statistical significance is an important criterion in interpreting the findings, it should not be the sole one. Some findings of this report involve broad patterns of differential substance use prevalence and dependence by race/ethnicity, patterns that show up in the estimates reported for most or all measures of substance use prevalence and dependence. Such persistent and recurring patterns in the data are often worth noting even when such trends and patterns are difficult to evaluate precisely on the basis of statistical significance tests.

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This page was last updated on May 19, 2008.