Selection bias related to parental consent in school-based survey research

The authors examined differences between students with and without written parental consent to take part in a sensitive health survey. The data were collected using a consent procedure combining ''active'' and ''passive'' response options. Two thousand seven hundred five 9th and 12th graders whose parents provided written consent completed a full survey. An identical survey, without sex-related questions, was completed by 3,533 students whose parents gave ''passive'' consent to this less sensitive version, Students with written consent were more likely to be White, to live in two-parent households, to have a grade point average of B or above, and to be involved in extracurricular activities. They were also more likely to have been exposed to health promotion interventions. Irregular seat belt use was lower in the written-consent group at both grade levels. Among 9th graders, cigarette smoking was less prevalent in the written-consent group, There were no significant differences in alcohol or illicit drug use.