[Characteristics of dropouts and participants in a twelve-year longitudinal research of Japanese elderly].
OBJECTIVE
The attrition of respondents in panel studies of the elderly can create bias in data analysis. The purposes of this study are two fold; 1) to examine characteristics of dropouts, from a particular panel lost except due to natural attrition (by death) by comparison with continuing participants in that wave, and 2) to assess representativeness of those actually continuing in a particular panel by comparison with those eligible for inclusion in that wave. Only those who died were excluded from the group of respondents at the baseline survey because they constituted natural attrition in this longitudinal survey.


METHODS
At baseline (1987), 2,200 individuals age 60+ from 3,288 national representative sample were interviewed. Non-response status to three contacts (1990, 1993, 1996) with the panel was examined in relation to variables included in the baseline interview. A number of characteristics of demographic background, health, life-style, and social relations obtained in the baseline survey (1987) were compared between those re-interviewed in a particular panel and subjects lost through unnatural attrition until that wave. To study the influence of unnatural attrition on variable distributions and each related factors of two health indicators (self-rated health and depressive symptoms), baseline responses were compared between those re-interviewed in a particular panel and all who were eligible to respond in that wave.


RESULTS
1) Dropouts lost to each wave were significantly older and had a lower level of social participation than persons remaining in that wave. Significant differences in health and life-style variables appeared between dropouts lost and continuing participants until third or later waves. 2) Continuing participants in a particular panel were likely to be younger, to be more physically, mentally, or socially healthy than those eligible to respond in the wave. Each related factors of two health indicators were almost same between those re-interviewed in a particular panel and those eligible to respond in that wave.


CONCLUSIONS
Dropouts in longitudinal research were found to appear nonrandomly. While distributions of age and health indicators in those re-interviewed were influenced by respondent attrition, related factors of health indicators may be free of bias that can be created by it.
Sugisawa
H
H
Department of Health Sociology, Tokyo Metropolitan Institute of Gerontology.
Kishino
H
H
Sugihara
Y
Y
Shibata
H
H
D000367:Age Factors; D000368:Aged; D006304:Health Status; D006801:Humans; D007407:Interviews as Topic; D007564:Japan; D008137:Longitudinal Studies; D008875:Middle Aged; D010352:Patient Dropouts