The declining response rate in the surveys is a major concern and can pose problems in generalizing data from the surveys to the Danish population. However, these surveys are essential, as the information collected cannot be gathered by means of official statistical registers. Hence, efforts to increase the response rate will be important in the forthcoming surveys.

Despite applying uniform methods, variations in the prevalence of antidepressant prescribing were obvious in the different populations. Database characteristics and clinical factors may both explain these variations.

The rate of adverse allergic skin reactions to hair dyes was higher than expected from patch-test studies. Only by studying the clinical types of adverse reactions to hair dyes will it be possible to gather a complete epidemiological picture of the nature and extent of the problems related to hair dye ingredients.