A systematic literature review of attrition between waves in longitudinal studies in the elderly shows a consistent pattern of dropout between differing studies.
OBJECTIVE
Longitudinal studies of the elderly are complicated by the loss of individuals between waves due to death or other dropout mechanisms. Factors that affect dropout may well be similar from one study to another. This article systematically reviews all large population-based studies of the elderly (published 1966-2002) that report on differences in individual characteristics between people who remain and people who dropout at follow-up.


METHODS
A systematic review of articles that investigate attrition after baseline interview.


RESULTS
Twelve studies were found that investigated dropout other than death using unadjusted, multivariable methods or both. The unadjusted analyses showed many significant factors related to attrition. Multivariable analyses showed two main independent factors were related to increased attrition: increasing age and cognitive impairment. People who were very ill or frail had higher dropout rates, and people in worse health were less likely to be recontactable.


CONCLUSIONS
Multivariable methods of analyzing attrition in longitudinal studies show consistent patterns of dropout between differing studies, with a small number of key relationships. These findings will assist researchers when planning studies of older people, and provide insight into the possible biases in longitudinal studies introduced by differential dropout.
Chatfield
Mark D
MD
Department of Public Health and Primary Care, Institute of Public Health, University Forvie Site, Robinson Way, Cambridge CB2 2SR, UK.
Brayne
Carol E
CE
Matthews
Fiona E
FE
D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015982:Bias; D003627:Data Interpretation, Statistical; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D015999:Multivariate Analysis; D010352:Patient Dropouts