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35 Prevalence of functional defecation disorders 1 IV criteria? (4) Are the survey instruments reliable and valid? (5) Are the analytic methods described/justified and appropriate? (6) Were the results reported in sufficient detail? Each question was scored on a 3-point scale (no (0), partial (1) or yes (2)) with higher scores representing better methodological quality. Data extraction The following data were extracted from each included study if possible: country where the study was performed, study design, type of population and sampling strategy, sample size, age range, sex distribution, method of data collection, definition of FDDs, overall prevalence of FC and FNRFI. If available, prevalence distributions according to sex, age and geographical location were extracted from each study. Moreover, if factors associated with FDDs (e.g., environmental, lifestyle and psychosocial factors) were reported, we evaluated these study findings. Statistical analyses Meta-analysis was performed using Comprehensive Meta-Analysis version 3 (Biostat Inc., Englewood, New Jersey). First, heterogeneity of included studies was assessed with the Cochrane-Q-statistic and I 2 test. A P -value < .10 and I 2 >50% were considered as significant heterogeneity. 16 Pooled prevalence rates for FC and FNRFI were calculated using a fixed effect model in case of no heterogeneity, otherwise the random effect model was applied. Subgroup analyseswith univariatemeta-regressionwere performed to assess the correlation between the prevalence and different study characteristics (e.g. geographical location, age of patients, and study quality score). Pooled odds ratios (OR) were calculated to assess the sex distribution. RESULTS Study selection and characteristics A total of 4,139 search results were identified (Figure 1). After screening titles and abstracts, 218 full text articles were assessed for eligibility and finally 37 articles were included. 17–53 Reasons for exclusion are presented in Figure 1. Out of the 37 articles included in the qualitative analysis, 35 studies were included in the meta-analysis. One longitudinal birth cohort study was excluded from the meta-analysis due to different reported prevalence rates within the same population, with different sample sizes due to loss to follow up at the last time point. 45 Another study was excluded because only percentages were reported without information on the number of cases. 48