14781-koppen

77 Functional defecation disorders and overweight 3 Data generation was performed independently by two authors (Drs Koppen and Kuizenga- Wessel). This process involved searching literature, data selection, and data extraction. In case of disagreement between these authors, consensus was reached by discussion or by consulting a third author (Dr Tabbers). To identify additional studies, reference lists of reviews and included studies were searched. Quality assessment Quality of the studies was assessed by using quality assessment tools from the National Heart, Lung, and Blood Institute (NHLBI); the choice for the applied tool was based on the study designs. We used 1 tool for observational cohort and cross-sectional studies and another tool for case-control studies. Both tools assessed the internal validity and risk of bias in a similar manner. 24 Two authors (Drs Koppen and Kuizenga-Wessel) applied these tools; they independently evaluated the items of the tools as “yes,” “no,” “not applicable,” “cannot determine,”or “not reported.”This was used to guide the overall rating for the quality of each study as “good,” “fair,” or “poor.” In case of disagreement, consensus was reached through discussion or by consulting a third author (Dr Tabbers). RESULTS A flowchart of the selection process is depicted in Figure 1. Eight studies were included, which were categorized into three groups: (1) studies that evaluated the prevalence of FDDs in obese children ( n =2; Table 2); (2) studies that evaluated the prevalence of overweight/ obesity in children with FDDs ( n =3; Table 3); (3) population-based studies assessing the association between FDDs and overweight/obesity ( n =3; Table 4). Studies were conducted in 6 different countries across 4 continents. Five studies were conducted in tertiary care centers, two studies were conducted in schools, and one study was conducted in primary care centers. In total, 5,442 children were described (1–20 years, 49.5% boys), this number reflects all study group children in the different studies and not only those with conditions of interest. Only three studies had a case-control design, and the total number of children in the control groups was 1,870 (2–20 years, 49.3% boys). The quality assessment for all included studies is presented in Tables 5 and 6.