Objective: To find a gold standard for crash risk assessment studies in the field of driving under the influence of psychoactive substances.
Methods: A questionnaire survey on methodological aspects concerning study designs was sent to researchers in the field of driving under the influence of psychoactive substances. The questionnaire was aimed at the 4 main study designs to assess the crash risk of driving under the influence: case-control studies, culpability studies, pharmaco-epidemiological studies, and experimental studies.
Results: The response rate for the questionnaire was 68 percent (N = 57). Forty-six percent of the respondents had a preference for assessing the crash risk by means of case-control studies, 35 percent by means of experimental studies, 14 percent by means of culpability studies, and 5 percent by means of pharmaco-epidemiological studies. In practice, however, only 51 percent of the researchers actually used the study type they preferred in theory. For the 4 most commonly used study designs, similarity rates varied from 66 to 81 percent for the theoretically preferred design and from 52 to 77 percent for the design that was actually applied.
Conclusions: Based on the results of the questionnaire survey, it can be concluded that despite several attempts in the past to standardize study design, there is still no common standard for assessing the crash risk of driving under the influence. The differences are not only caused by practical, legal, financial, or ethical issues but also by differences between researchers concerning their theoretically preferred study design.