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Investigation of bias due to loss of participants in a Dutch multicentre prospective spinal cord injury cohort study
OBJECTIVE: To determine bias due to loss of participants (attrition bias) in a prospective cohort study.
DESIGN: A multi-centre prospective cohort study.
SUBJECTS: A total of 225 individuals with a spinal cord injury from 8 Dutch rehabilitation centres.
METHODS: Participants were considered non-participants when no information was collected at the measurement one year after discharge from inpatient rehabilitation. Using bivariate tests participants and non-participants were compared regarding personal, lesion, function and functional characteristics determined at the beginning of inpatient rehabilitation and at discharge. A logistic regression was performed to determine which characteristics predict participation at one year after discharge.
RESULTS: Of the participants at the start of the study, 31% (n = 69) did not perform the tests one year after discharge from inpatient rehabilitation. Variables associated with study participation one year after discharge were: higher level of education, higher well-being score at the start of rehabilitation, and a shorter length of stay in hospital and rehabilitation centre at discharge of inpatient rehabilitation.
CONCLUSION: Selective attrition in the longitudinal study might have led to an over-estimation of some of the results of the measurement one year after discharge from inpatient rehabilitation.
Sonja de Groot, Janneke A. Haisma, Marcel W.M. Post, Floris W.A. van Asbeck, Lucas H.V. van der Woude
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