Fig. 1From: Recreational Athletes’ Use of Performance-Enhancing Substances: Results from the First European Randomized Response Technique SurveyLiterature search procedure. Combinations of terms were used for the search process in the literature review. Categories were linked with AND while search terms within the categories were linked with OR. The term combinations are made up of Who? (target group of the study), What? (used substances in a study), and How? (used method of the study). The respective terms of the category are listed in each case as example terms in the figureBack to article page