1. Age as the time dimension:
Albanese, E., Matthews, K.A., Zhang, J., Jacobs, D.R., Whitmer, R.A., Wadley, V.G., Yaffe, K., Sidney, S. and Launer, L.J., 2016. Hostile attitudes and effortful coping in young adulthood predict cognition 25 years later. Neurology, 86(13), pp.1227-1234.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4818565/pdf/NEUROLOGY2015672964.pdf
i. Research Question: Are high levels of hostility and effortful coping in early adult life (under the age of 30 years) associated with lower cognitive function in early/midlife?
ii. Study Sample: The Coronary Artery Risk Development in Young Adults Study (CARDIA)
iii. Longitudinal Design: CARDIA sampled 5,115 participants between the ages of 18 and 30 from 4 US centers in 1985-1986, and re-examined the cohort at years 2, 5, 7, 10, 15, 20, and 25. For this study, the analysis was restricted to the 3,126 participants with data for all covariates at year 25 (89% of the sample).
iv. Analysis Approach: Multivariable linear regressions were used to assess the association of midlife (year 25) cognitive function to quartiles of psychological characteristics, adjusting for age, race, and sex.
2. Time since study enrollment as the time dimension:
Khondoker, M., Rafnsson, S.B., Morris, S., Orrell, M. and Steptoe, A., 2017. Positive and Negative Experiences of Social Support and Risk of Dementia in Later Life: An Investigation Using the English Longitudinal Study of Ageing. Journal of Alzheimer's disease: JAD.
i. Research Question: Do close social relationships in later life affect risk of developing dementia?
ii. Study Sample: The English Longitudinal Study of Ageing (ELSA), a panel study of community dwelling individuals over the age of 50 in England
iii. Longitudinal Design: ELSA participants were surveyed every two years using computer-assisted personal interviews for up to six waves covering a period of 10 years. The outcome was defined as time-to-dementia from the start date of the ELSA study.
iv. Analysis Approach: Because data collection occurred in two year intervals, neither time-to-dementia for incident cases nor censoring time were known. Both were treated as interval censored in proportional hazards regression models to estimate the risk of dementia by the end of the follow-up period.
3. Time since (and prior to) installation of Pokémon GO as the time dimension:
Howe, K.B., Suharlim, C., Ueda, P., Howe, D., Kawachi, I. and Rimm, E.B., 2016. Gotta catch’em all! Pokémon GO and physical activity among young adults: difference in differences study. BMJ, 355, p.i6270.
https://www-ncbi-nlm-nih-gov.ucsf.idm.oclc.org/pmc/articles/PMC5154977/
i. Research Question: Does playing Pokémon GO affect the number of steps taken daily?
ii. Study Sample: Survey participants of the Amazon Mechanical Turk (MTurk), a recruitment of online workers who receive a small compensation for completing tasks, between the ages of 18 to 35 residing in the US with an iPhone 6 series smartphone.
iii. Longitudinal Design/Analysis Approach: Participants were asked to upload screenshots of their number of steps daily while carrying their iPhone for each day, which are recorded by default in the Health application of the iPhone 6 series, as well as screenshots of their Pokemon GO application, which shows the installation date and was independent of survey recruitment. The authors conducted a difference in difference analysis by comparing the average number of steps taken each day for each of the four weeks prior to installation compared to the steps during each of the six weeks after installation in players of Pokémon GO and non-players, respectively. For non-players, the median date of installation among players was used as the cutoff for the difference-in-differences analysis. Multivariate regression was used, and the estimate of change in number of steps was obtained using an interaction indicator for playing status and week after installation of the game.