Abstract
During the preparation of a paper on the number of persons killed and casualty accidents in the three years before and after the introduction of Sunday alcohol scales in Perth by the same author, a number of methodological issues arose. In view of the interest in evaluative studies on the topic of alcohol and traffic safety, it its likely that other researchers could also encounter these issues. Accordingly, this paper discuss these issues under the four headings of experimental design, internal validity, external validity and number of experimental conditions.