14781-koppen

64 Chapter 2 METHODS The design of this study was based on previous studies in school children, performed and described by our group. 15,16 In short, between February and October 2014, an invitation package was sent to the families of 4,093 children between 8 and 18 years of age attending schools in 4 main regions of Colombia's mainland; the Andean region (the mountains), the Caribbean region (adjacent to the Caribbean Sea), the Pacific region (adjacent to the Pacific Ocean), and the Amazon region (tropical rainforest). Children were invited through the Obesity and Overweight monitoring program (Programa de Seguimiento de la Obesidad y del Sobrepreso) by the Gastrohnup Research Group at the University del Valle (Cali, Colombia) and the Functional International Digestive Epidemiological Research Survey program. Parents gave written informed consent and all children provided assent to participate. A screening questionnaire was completed by the parents to identify and exclude children who had a history of known organic medical conditions. Children who were underweight (body mass index [BMI] z-score <−2) were excluded from further analyses because of the possibility of undiagnosed organic diseases. Children were also excluded from the analyses if they had a diagnosis of another functional gastrointestinal disorder (not functional constipation) and if missing data hindered the calculation of the BMI z-score or determination of the occurrence of functional gastrointestinal disorders. The Ethics Committee of Clinical Investigation from the University del Valle (Cali, Colombia) and local school authorities approved the study. Demographic data were obtained through questionnaires. Anthropometric measurements of weight, height, and BMI were obtained following World Health Organization (WHO) guidelines 17 ; weight (in kilograms) was measured with the child standing on an electronic scale, height (in centimeters) was measured using an adjustable stadiometer. BMI was calculated as weight in kilograms divided by the square of the height in meters (kg/m 2 ). BMI z-scores were corrected for age and sex and used to define weight categories according to the WHO cut-off values 18 ; BMI z-scores below −2 were considered underweight, between −2 and +1 as normal weight, between +1 and +2 as overweight, and above +2 as obesity. A Spanish translation of the Questionnaire on Pediatric Gastrointestinal Symptoms–Rome III Version (QPGS-RIII) was used to diagnose functional constipation and other functional gastrointestinal disorders. The QPGS-RIII is a validated questionnaire for diagnosing functional gastrointestinal disorders in children. The use of the Spanish translation of the QPGS-RIII has been previously described. 19 To ensure children's comprehension, the investigators reviewed the questionnaire with the children during a presentation before administration and a member of the research team was available for questions while the participants completed the questionnaire.