摘要：Objectives . This investigation examined the effectiveness of intensive efforts to include frequently absent students in order to reduce bias in classroom-based studies. Methods . Grade 10 students in 13 New York City high schools (n = 2049) completed selfadministered confidential surveys in 4 different phases: a 1-day classroom capture, a 1-day follow-up, and 2 separate 1-week follow-ups. Financial incentives were offered, along with opportunities for out-of-classroom participation. Results . Findings showed that frequently absent students engaged in more risk behaviors than those who were rarely absent. Intensive efforts to locate and survey chronically absent students did not, however, significantly alter estimates of risk behavior. Weighting the data for individual absences marginally improved the estimates. Conclusions . This study showed that intensive efforts to capture absent students in classroom-based investigations are not warranted by the small improvements produced in regard to risk behavior estimates. At present, most research on adolescent risk behaviors is school based 1, 2 and involves either a 1- or 2-day classroom-based survey methodology, with investigators surveying students in the classroom at a specific time on a given day. In urban public high schools with high rates of daily absenteeism, these survey protocols have the potential to produce considerable bias in that large numbers of students are not included. Rates of classroom absenteeism (i.e., students skipping individual classes) tend to be even higher and more difficult to measure accurately. Furthermore, students who are chronically absent represent an additional challenge to obtaining representative data. Researchers have relied on a variety of techniques, including tracking respondents through friends, conducting intensive follow-up sampling, and weighting data according to self-reported absences, to address bias resulting from absenteeism (P. M. O'Malley, meeting minutes, November 23, 1998). 2, 3 The present study was designed to answer the following questions: Do students who are absent from the classroom when data are collected differ on a variety of demographic and behavioral variables from students captured in a classroom-based sample? If such differences exist, does weighting based on selfreported absenteeism provide an accurate estimate of risk behavior for the entire student population?
