to the interview. A sample of youth in grades 6 through 12 was also interviewed following the completion of the parent interview about the youth. This report was based on the responses of students in grades 6 through 12.Response RatesData ReliabilityEstimates produced using data from the NHES:93 are subject to two types of error, sampling and nonsampling errors. Nonsampling errors are errors made in the collection and processing of data. Sampling errors occur because the data are collected from a sample rather than a census of the population.Nonsampling ErrorsNonsampling error is the term used to describe variations in the estimates that may be caused by population coverage limitations and data collection, processing, and reporting procedures. The sources of nonsampling errors are typically problems like unit and item nonresponse, the differences in respondents' interpretations of the meaning of the questions, response differences related to the particular time the survey was conducted, and mistakes in data preparation.In general, it is difficult to identify and estimate either the amount of nonsampling error or the bias caused by this error. In the NHES survey, efforts were made to prevent such errors from occurring and to compensate for them where possible. For instance, during the survey design phase, focus groups and cognitive laboratory interviews were conducted for the purpose of assessing respondent knowledge of the topics, comprehension of questions and terms, and the sensitivity of items. The design phase also entailed over 500 staff hours of CATI instrument testing and a pretest in which over 275 interviews were conducted.An important nonsampling error for a telephone survey is the failure to include persons who do not live in households with telephones. About 92 percent of all students in grades 3 through 12 live in households with telephones. Estimation procedures were used to help reduce the bias in the estimates associated...
