Estimating age change in list recall in asset and health dynamics of the oldest-old: the effects of attrition bias and missing data treatment

Attrition from longitudinal ageing studies and performance across domains of cognitive functioning: an individual participant data meta-analysis

OBJECTIVES

This paper examined the magnitude of differences in performance across domains of cognitive functioning between participants who attrited from studies and those who did not, using data from longitudinal ageing studies where multiple cognitive tests were administered.

DESIGN

Individual participant data meta-analysis.

PARTICIPANTS

Data are from 10 epidemiological longitudinal studies on ageing (total n=209 518) from several Western countries (UK, USA, Mexico, etc). Each study had multiple waves of data (range of 2-17 waves), with multiple cognitive tests administered at each wave (range of 4-17 tests). Only waves with cognitive tests and information on participant dropout at the immediate next wave for adults aged 50 years or older were used in the meta-analysis.

MEASURES

For each pair of consecutive study waves, we compared the difference in cognitive scores (Cohen's d) between participants who dropped out at the next study wave and those who remained. Note that our operationalisation of dropout was inclusive of all causes (eg, mortality). The proportion of participant dropout at each wave was also computed.

RESULTS

The average proportion of dropouts between consecutive study waves was 0.26 (0.18 to 0.34). People who attrited were found to have significantly lower levels of cognitive functioning in all domains (at the wave 2-3 years before attrition) compared with those who did not attrit, with small-to-medium effect sizes (overall d=0.37 (0.30 to 0.43)).

CONCLUSIONS

Older adults who attrited from longitudinal ageing studies had lower cognitive functioning (assessed at the timepoint before attrition) across all domains as compared with individuals who remained. Cognitive functioning differences may contribute to selection bias in longitudinal ageing studies, impeding accurate conclusions in developmental research. In addition, examining the functional capabilities of attriters may be valuable for determining whether attriters experience functional limitations requiring healthcare attention.

Attrition in Longitudinal Data is Primarily Selective with Respect to Level Rather than Rate of Change

OBJECTIVES

An important question in longitudinal research is whether the individuals who discontinue participation differ in their level of, or their change in, cognitive functioning relative to individuals who return for subsequent occasions.

METHODS

Performance in five cognitive domains was examined in nearly 5000 participants between 18 and 85 years of age who completed between one and five longitudinal occasions.

RESULTS

Little or no differences in cognitive performance were apparent between young adults who did or did not return for subsequent longitudinal occasions. However, among adults above about 45 years of age, returning participants had higher levels of cognitive performance, but approximately similar magnitude of longitudinal change, as participants completing fewer occasions.

CONCLUSIONS

These results suggest that generalizability of longitudinal comparisons may be restricted to individuals with relatively high levels of cognitive functioning, but that rates of cognitive change are nearly comparable for individuals completing different numbers of longitudinal occasions.

Age, HIV status, and research context determined attrition in a longitudinal cohort in Nigeria

OBJECTIVES

We explored determinants of attrition in a longitudinal cohort study in Nigeria.

STUDY DESIGN AND SETTING

We enrolled 1,020 women into a prospective study. Of these, 973 were eligible to return for follow-up. We investigated the determinants of attrition among eligible women using a sequential mixed methods design. We used logistic regression models to compare the baseline characteristics of responders and nonresponders. At the end of the parent study, we conducted four focus group discussions and eight key informant interviews with nonresponders.

RESULTS

Of the 973 women included in the quantitative analysis, 26% were nonresponders. From quantitative analysis, older women were less likely to drop out than younger women (reference: women ≤30 years; OR 0.46; 95% confidence interval [CI] 0.30-0.70, P < 0.001 women 31-44 years; and OR 0.31; 95% CI 0.17-0.56, P < 0.001 women ≥45 years). HIV-positive women were also less likely to drop out of the study (OR 0.45; 95% CI 0.33-0.63, P < 0.001). From qualitative analysis, contextual factors that influenced attrition were high cost of participation, therapeutic misconceptions, inaccurate expectations, spousal disapproval, unpleasant side effects, challenges in maintaining contact with participants, and participant difficulties in locating the study clinic.

CONCLUSION

Several participant-, research-, and environment-related factors influence attrition. Retention strategies that address these barriers are important to minimize attrition.

Selectivity of attrition in longitudinal studies of cognitive functioning

OBJECTIVES

Identify characteristics distinguishing people who do and do not continue to participate in a longitudinal study and determine whether the longitudinal changes for people who continue are representative of the changes that would have occurred had longitudinal data been available from all of the initial participants.

METHOD

Moderately large samples of returning (N = 2,082) and nonreturning (N = 1,698) participants across a wide age range (i.e., 18-97 years of age) performed a battery of cognitive tests and completed personality and mood questionnaires. Differences between the groups were examined with multiple regression analyses with age, returner status, and their interaction as predictors.

RESULTS

Compared with participants who did not return, returning participants at the initial occasion had higher levels of each cognitive ability and of certain personality characteristics (e.g., agreeableness and openness), but many of the differences were only apparent among adults older than 50 years of age. Importantly, there was no evidence that the longitudinal change for nonreturning participants would have been different from that among the participants who did return.

DISCUSSION

The phenomenon of selective attrition is more complex than often assumed, and it may not necessarily limit the generalizability of longitudinal comparisons.

Influence of age on practice effects in longitudinal neurocognitive change

OBJECTIVE

Longitudinal comparisons of neurocognitive functioning often reveal stability or age-related increases in performance among adults under about 60 years of age. Because nearly monotonic declines with increasing age are typically evident in cross-sectional comparisons, there is a discrepancy in the inferred age trends based on the two types of comparisons. The current research investigated the role of practice effects in longitudinal comparisons on the discrepancy.

METHOD

Longitudinal data over an average interval of 2.5 years were available on five abilities (i.e., reasoning, spatial visualization, episodic memory, perceptual speed, vocabulary) in a sample of 1,616 adults ranging from 18 to over 80 years of age. Practice effects were estimated from comparisons of the performance of people of the same age tested for either the first or second time, after adjusting for the possibility of selective attrition.

RESULTS

Increased age was associated with significantly more negative longitudinal changes with each ability. All of the estimated practice effects were positive, but they varied in magnitude across neurocognitive abilities and as a function of age. After adjusting for practice effects the longitudinal changes were less positive at younger ages and slightly less negative at older ages.

CONCLUSIONS

It was concluded that some, but not all, of the discrepancy between cross-sectional and longitudinal age trends in neurocognitive functioning is attributable to practice effects positively biasing the longitudinal trends. These results suggest that the neurobiological substrates of neurocognitive functioning may change across different periods in adulthood.

Not your parents' test scores: cohort reduces psychometric aging effects

Increases over birth cohorts in psychometric abilities may impact effects of aging. Data from 2 cohorts of the Long Beach Longitudinal Study, matched on age but tested 16 years apart, were modeled over ages 55-87 to test the hypothesis that the more fluid abilities of reasoning, list and text recall, and space would show larger cohort differences than vocabulary. This hypothesis was confirmed. At age 74, average performance estimates for people from the more recently born cohort were equivalent to those of people from the older cohort when they were up to 15 years younger. This finding suggests that older adults may perform like much younger ones from the previous generation on fluid measures, indicating higher levels of abilities than expected. This result could have major implications for the expected productivity of an aging workforce as well as for the quality of life of future generations. However, cohort improvements did not mitigate age declines.