1.4 Limitations of the Data

There are several limitations to the data used in this study. First, the data are mostly self-reported, including the main analysis variables (i.e., whether or not the respondent used drugs and the characteristics of their workplaces). Behavioral estimations may be inaccurate or biased, particularly for substance abuse behaviors. Second, the sample excludes active military personnel, U.S. citizens living abroad, residents of institutional settings, (e.g., prisons and hospitals), and homeless persons not living in a shelter at the time of the survey. A third limitation is the relatively rare occurrence of certain workplace characteristics (such as involvement of the respondent in an accident during the past 30 days). These limitations mean that to retain statistical precision, the respondents can not be divided into smaller analytical subgroups.