Age as the time dimension: Pearson JD, Morrell CH, Brant LJ, Landis PK, Fleg JL. Age-associated changes in blood pressure in a longitudinal study of healthy men and women. J Gerontol A Biol Sci Med Sci. 1997;52(3):M177-83.
a. Research question: to assess an association between aging and increases in blood pressure among healthy men and women.
b. Study sample: Participants from the Baltimore Longitudinal Study of Aging (BLSA). 1,307 men (age 17-97) and 333 women (age 18-93) who have been screened for health problems or medications that affect blood pressure.
c. Longitudinal design: cohort followed for 32 years
d. Analysis approach: they used longitudinal mixed-effects regression models to estimate the age-associated changes in blood pressure among the men and women in their population.
Time since study enrollment as the time dimension: Riley E, Evans J, Hahn J, Davidson P, Lum P, Page K. A Longitudinal Study of Multiple Drug Use and Overdose among Young People Who Inject Drugs. Am J Pub Health. 2016; 106(5):915-7.
a. Research question: is there an association between multidrug use and nonfatal overdose among young people in San Francisco?
b. Study sample: 173 injection drug users younger than 30 years old living in SF
c. Longitudinal design: potential participants were recruited between April 2012 and February 2014 to participate in a longitudinal cohort study of young injectors, UFO (“U Find Out”). Participants completed a visit every 3 months in which they self-reported overdose events and a set of other factors including polysubstance use through an ACASI (computerized interview) and HCV test.
d. Analysis approach: The research team used longitudinal logistic regression models fir by generalized estimating equations to estimate the effects of polysubstance use on overdose rates.
One other possible time dimension (time since retirement): Wu C, Odden M, Fisher G, Stawski R. Association of retirement age with mortality a population-based longitudinal study among older adults in the USA. BMJ. 2015. https://ucsf.idm.oclc.org/login?url=http://dx.doi.org/10.1136/jech-2015-207097
a. Research question: Is there an association between retirement age and mortality among healthy and unhealthy retirees and is this relationship modified by SES.
b. Study sample: 2,956 retirees from the Health and Retirement Study
c. Longitudinal design: tracked retirement age and reason for retirement from the Health and Retirement Study. Participants were followed from 1992-2010 – during which time 2956 participants retired. They were tracked over the course of the study and death was recorded.
d. Analysis approach: association of retirement age with all-cause mortality was analyzed using the cox model, adjusting for sociodemographics.