Impact of various questionnaires on the prevalence of erectile dysfunction. The ENIGMA-study

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Abstract
The prevalence estimates of erectile dysfunction (ED) vary considerably across studies. These differences may be attributed to used definitions of ED. Quantitative data on the effect of different definitions of ED on the prevalence are lacking, because precise information on the used definition and questionnaire is often absent. Aim of this study was to quantify the effect of using different questionnaires for ED on the prevalence estimates. In all, 5721 mail surveys on sexual problems and ED were sent to all men (aged>18 y) in 12 general practices in the middle of the Netherlands of which 2117 were completed. The questionnaire contained Enigma (WHO), International Index of Erectile Function (IIEF), Cologne Erectile Inventory (KEED) and one question (Boxmeer, Krimpen). The prevalence of ED based on the various questionnaires and the effect of these questionnaires on risk factor relationships was compared. IIEF gave the highest age specific and overall ED prevalence, KEED the lowest. The difference in prevalence was 16.8%. The agreement (kappa coefficient) between the various ED definitions varied from 0.52 (IIEF & KEED) to 0.95 (Enigma & Boxmeer). The number of risk factor relations were similar for the Dutch studies, reduced for the IIEF and KEED. This study provides evidence that differences in questionnaires to assess ED have a considerable effect on the (age specific) prevalence estimates and little on the risk factor relations. The number of questions of the survey appears not to be responsible for differences in the prevalence of ED and risk factor relations, however they affect the response rate. Uniform use is strongly recommended, since a 'golden standard' for ED assessment (by questionnaire) is lacking. A short questionnaire with one or two questions is recommended for example the one from the Boxmeer-study. These data may be used to adjust (age-specific) prevalence rates comparing ED prevalence in the open population across studies.