Attrition and bias in a longitudinal population-based study on back pain

Background and Aims: Potential bias because of attrition has received little attention in primary studies on back pain. This study aims to identify those back pain related indicators most susceptible to bias and to discuss practical consequences for back pain research. Methods: Analyses were based on a population-based longitudinal multi-centre postal back pain survey with two postal follow-up measurements within two years. The baseline sample comprised 9,263 subjects. Different sets of measures at entry were used to predict subsequent attrition: Socio-demographic variables, indicators of back pain, health relat…