The "Technical Notes" found in appendix A present information on the primary data sources used in this report. Many of the data sources used in this report are sample surveys. Information presented from sample surveys has differing degrees of reliability. Survey summaries may differ from the actual values for the population under study due to a number of sources contributing error to the estimates. This report states differences in comparisons of groups or in trends in the data over time only if they are greater than the differences that would be likely to result due to chance. (In statistical terms, for this report the impact of sampling error is accounted for by testing at the 95 percent confidence level any individual comparisons presented.) Where possible, analysts have also considered the impact of nonsampling errors such as incomplete coverage and nonresponse.