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Statistics from surveys are subject to sampling and nonsampling error. All comparisons presented in this report have taken sampling error into account and meet the U.S. Census Bureau's standards for statistical significance. Nonsampling errors in surveys may be attributed to a variety of sources, such as how the survey was designed, how much nonresponse occurs, how respondents interpret questions, how able and willing respondents are to provide correct answers, and how accurately the answers are coded and classified. The Census Bureau employs quality control procedures throughout the production process including the overall design of surveys, the wording of questions, review of the work of interviewers and coders, and statistical review of reports.
The Survey of Program Dynamics employs ratio estimation, whereby estimates are adjusted to independent measures of the national population by age, race, sex, and Hispanic origin. This weighting partially corrects for bias due to undercoverage, but how it affects different variables in the survey is not precisely known. Moreover, biases may also be present when people who are missed in the survey differ from those interviewed in ways other than the categories used in weighting (age, race, sex, and Hispanic origin). All of these considerations affect comparisons across different surveys or data sources.
Users of the Survey of Program Dynamics (SPD) data should be aware of some special concerns regarding the accuracy of its estimates and take these into consideration when interpreting the survey results. These concerns are:
