First record: a methodological approach to counter sampling bias

One goal of survey research is to optimize sampling procedures so that the collected data will produce accurate population estimates. In this context, sampling bias is a primary threat to a study's validity. If individuals who do not respond are a random sample of the population, then the estimates obtained from such a subsample are unbiased. However, as the percentage of nonrespondents increases, the assumption of unbiased estimation becomes increasingly tenuous. At this point an investigator has two choices: delete all subjects who have not provided data as part of the first data collection, or allow a respondent's point of entry to define his baseline measures for the study. No previous discussion of the latter option has been noted in the methods literature. Therefore the authors have termed this approach to baseline the "first record". Conditions under which the "first record" technique would be appropriate or inappropriate are discussed.