To clarify the factors that contribute toward the gradual drop-out from society in older adults, this study defined stages of follow-up difficulty in a longitudinal study and examined the characteristics of the individuals in each stage of follow-up difficulty. Since there are no existing studies that defined follow-up difficulty for non-respondents of a longitudinal survey, the present study is novel and offers a valuable contribution to the theory. Many previous studies have suggested that respondents’ tendency to drop out from a longitudinal study may be affected by poor health and SES at the baseline survey (1, 3-5, 16, 17). Therefore, to compare the findings obtained in this study with those of previous studies, we first examined whether the FL1 respondents—those who did not dropout from the longitudinal survey in this study—had similar results to those of previous studies. The FL1 respondents showed statistically significant differences in age, IADL score, participation in hobby and sports groups, self-rated health, and perceived financial status compared to the other stages of follow-up difficulty. This suggests that the health condition and SES, physical function, and social activity levels were high in those who did not drop out.
These results are concordant with several previous studies that examined attrition in longitudinal studies (1, 3-5, 17). Therefore, although this study was conducted in a cohort of community-dwelling older adults in Japan, the results are generalizable to some extent.
Follow-up surveys—which were gradually made easier to answer—were conducted on those who dropped out of this study’s longitudinal survey and we investigated each response rate at the different stages. As a note, these gradually changing follow-up surveys have not been conducted in the previous studies and no previous studies have focused on follow-up surveys from this perspective. The response rates of each follow-up survey were 47.5% (462/971) for the simplified mail survey (FL2), 46.9% (234/499) for the postcard survey (FL3), and 32.2% (84/261) for the home visit survey (FL4) respectively. This indicates that even if people dropped out from the survey once, approximately 30–50% of these individuals responded to the follow-up surveys that were altered to make them easier to answer. These results can be utilized to conduct follow-up surveys on non-responders of a longitudinal mail survey by changing the survey methods.
Contrary to our assumption that answering the follow-up questions of the surveys would be progressively easier when changing the survey method by implementing simplified mail, postcards, and home visit surveys, the response rate gradually declined. This indicates that the more difficult the follow-up is, the more problematic it is to obtain responses, even if the surveys themselves become easy to answer. Therefore, to explore the reasons for this decline, we examined the characteristics associated with the stage of follow-up difficulty.
It was observed that the IADL gradually decreased along with the stage of follow-up difficulty. Although the results concerning some social activities were not consistent, it can be suggested that the participation rate in activities would also decrease along with the follow-up difficulty. The results further showed that the percentage of isolation increased with the increase in follow-up difficulty. A similar tendency was observed concerning health and economic status. Therefore, the stage of follow-up difficulty defined in this study can be regarded to reflect the decline in physical function and social activity that are related to restricted social participation.
Next, we examined the baseline factors that determined the stage of follow-up difficulty. The factors involved in each stage were participation in hobby groups for the FL2 and FL3 respondents, participation in sports groups for the FL4 respondents, and participation in neighborhood associations and isolation for the NR. Similar results were obtained concerning the FL4 and NR groups after the covariates adjustment. These results were considered to be more robust than those of FL2 and FL3. A relatively small percentage of people (4.8%) participated in sports groups in FL4, which could indicate that many people who dislike participating in sports were included in this stage. Physical activity may also be low in this stage, making it difficult for the respondents to answer even the postcard survey because of poor physical function. This may be the reason they responded only to the home visit survey. Moreover, a decline in cognitive function makes it difficult to respond to mail. Therefore, it is possible that the group who could not respond to the postcard survey and responded to the home visit survey instead may include persons with cognitive decline. Several studies have reported cognitive function as a factor of attrition in longitudinal studies (1).
In the NR group, there were many people with low social interaction, which contributes greatly to isolation. The participation rate for even local activities like the neighborhood association was low. This means that the NR group included many people with low social interaction and with poor social participation.
On the other hand, social participation did not prove to be factors in the FL2 and FL3 groups after adjusting the covariates. It was in fact IADL that proved to be the factor more significantly associated with these stages. This suggests that the decline of daily living function made it difficult for people to respond in these stages. As Nemoto et al. (11) reported, social activity can be restricted by IADL disability and the decline in baseline IADL may restrict future social participation in persons of those stages.
Based on these results, we conclude that the factors associated with each stage of follow-up difficulty are: 1) their activities start to be restricted by a decline in IADL in the FL2 and FL3 stages, 2) they dislike taking part in physical activity such as sports in the FL4 stage, and 3) they are more socially isolated, not belong to even a neighborhood association owing to be low social interaction in the NR group. Older adults to which these factors apply are at the risk of restricted social participation in the future. The result of this study also showed that the appropriate support needed to enable older adults to respond to longitudinal surveys differed among the stages of follow-up difficulty. The findings obtained in this study will be useful for preventing not only drop-out from surveys in a longitudinal study but also to prevent gradually restricted social participation among older adults.
The limitations of this study are as follows: although the characteristics at the baseline of each stage of follow-up difficulty were examined, the characteristics at each follow-up survey were not compared to each other. However, we did determine that health outcomes—such as self-rated health and incidence of requirement of long-term care—differ for each of the follow-up surveys and between the stages of follow-up difficulty. These results will be reported in a future study. Another limitation of this study is that factors concerning non-respondents like moving away or death were accurately examined using resident cards only for the FL2 survey. As for the other follow-up surveys, we identified the moving away or death factors only by information from the participants or their family members. Therefore, non-responders for the FL3 group and later groups may include more moves and deaths. However, the surveys after the FL3 survey were conducted within one year and the impact on the results obtained in this study would be small. Since this study was a longitudinal mail survey, it was not possible to assess details concerning educational status, work, and cognitive function, which have been indicated by prior studies to be associated with increased rates of attrition. In future studies, it is necessary to determine whether these factors are associated with follow-up difficulty.