Analysis of Drop-outs in a 2-year Follow-up of individuals exposed to Whiplash Trauma

Abstract: Most studies that investigate the relationship between temporomandibular disorders (TMD) and whiplash are cross-sectional, but in order to identify risk factors prospective studies are needed. The reliability of prospective studies is dependent on representative follow-up groups. The prospective study “ProNeck” investigated possible risk factors for devolvement of TMD following a whiplash trauma by comparing cases to controls within one month following whiplash trauma and after two years. The aim of the present study was to investigate whether dropouts from “ProNeck” differed in baseline symptoms from individuals attending the two-year follow-up. A second aim was to reduce number of dropouts by offering a short-version follow-up questionnaire. In total, baseline data from 217 cases and controls who participated in the two-year follow-up was compared with baseline data from 65 drop-outs. Parameters analysed were gender, age, Neck Disability Index, intensity of jaw and neck pain on the Numerical Rating Scale, screening questions on jaw pain and dysfunction, depression and physical symptoms. The short follow-up questionnaire containing five key questions was sent to 13 participants who did not attend the two-year follow-up. No significant difference for any of the analysed parameters was found when comparing baseline data between individuals that participated in the two-year follow-up and dropouts. For the shortened follow-up questionnaire, only one individual completed the questionnaire. The results of the dropout analysis strengthen the reliability and value of the prospective study "ProNeck". The low response-rate of the short-follow up questionnaire indicates that there is little gain trying to reduce dropouts in prospective studies by offering short-version questionnaires.