đau bụng tái phát: một nghiên cứu lĩnh vực của trẻ em học. Arch Dis trẻ em năm 1958; 33:165-70. 40. Feldman W, Rosser W, McGrath P. thường xuyên đau bụng ở trẻ em. Fam Physician 1988; 34:629-30. 41. Rosenberg AJ. Táo bón và encopresis. In: các biên tập viên của Wyllie R | 274 Evidence-Based Pediatrics were randomly assigned to receive counseling about the risks of cycling and the benefits of helmets and were also given pamphlets about bicycle safety and helmets. Almost 90 percent of the participants were successfully contacted by telephone 2 to 3 weeks later. Among the intervention group percent had purchased a helmet compared with percent of the control group. The high proportion of control parents having purchased a helmet was thought to be due to either the testing effect of the survey or to the postinjury motivation to buy a helmet. The testing effect the authors describe may have been a Hawthorne effect where subjects alter their behavior due to participation in a study or a form of contamination where the control group also received counseling about bicycle helmet use by completing the A similar study was then conducted in children presenting to their family physician or pediatrician for routine ambulatory care. The patients were randomly assigned to receive helmet promotion counseling and pamphlets. When parents were contacted 2 to 3 weeks later percent of the intervention group had purchased helmets compared with percent of the control group. The surprising number of control families having purchased a helmet within 2 to 3 weeks of the office visit may have been due to the testing effect of the survey or due to the concurrent community-based promotion of The authors discuss the possibility that the families responding positively to the intervention and perhaps to the survey itself were innovators or early adapters who were ready to buy a helmet and needed little persuasion to do so. The third randomized controlled trial was designed to determine whether a copayment for a helmet would affect helmet use when compared with providing helmets free of charge for children between 6 and 12 years of age who reported riding bicycles but not owning a Families were also counseled .
