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85 Functional defecation disorders and overweight 3 TABLE 6. NHLBI quality assessment of case-control studies Kavehmanesh et al. Teitelbaum et al. Wagner et al. 1. Was the research question or objective in this paper clearly stated and appropriate? Yes Yes Yes 2. Was the study population clearly specified and defined? Yes Yes Yes 3. Did the authors include a sample size justification? No No No 4. Were controls selected or recruited from the same or similar population that gave rise to the cases (including the same timeframe)? Yes CD CD 5. Were the definitions, inclusion and exclusion criteria, algorithms or processes used to identify or select cases and controls valid, reliable, and implemented consistently across all study participants? No Yes Yes 6. Were the cases clearly defined and differentiated from controls? No Yes Yes 7. If less than 100 percent of eligible cases and/or controls were selected for the study, were the cases and/or controls randomly selected from those eligible? NR NR NR 8. Was there use of concurrent controls? CD CD CD 9. Were the investigators able to confirm that the exposure/risk occurred prior to the development of the condition or event that defined a participant as a case? CD CD CD 10. Were the measures of exposure/risk clearly defined, valid, reliable, and implemented consistently (includingthe same time period) across all study participants? CD No Yes 11. Were the assessors of exposure/risk blinded to the case or control status of participants? NR NR NR 12. Were key potential confounding variables measured and adjusted statistically in the analyses? If matching was used, did the investigators account for matching during study analysis? No No No Rating Poor Poor Fair Available at: http://www.nhlbi.nih.gov/health-pro/guidelines/in-develop/cardiovascular-risk-reduction/tools/case-control. CD, cannot determine; NA, not applicable; NR, not reported. DISCUSSION This systematic review could not confirm or refute the association between FDDs and overweight/obesity because results are conflicting across the studies. Both studies in obesity clinics revealed a high prevalence (21%–23%) of FC compared with the general population (3%–16%), and 2 out of 3 case-control studies in children with defecation disorders revealed a higher prevalence of overweight and obesity in patients with FDDs (12%–33% and 17%–20%, respectively) compared with controls (13%–23% and 0%–12%, respectively). On the other hand, only one of three population-based studies revealed evidence for an association.