#### Abstract

Objectives: To estimate the number of persons in a cohort who are sick, over time.

Methods: We calculated the number of sick persons in the Cardiovascular Health Study (CHS), a cohort study of older adults followed up to 14 years, using eight definitions of “healthy” and “sick”. We projected the number in each health state over time for a birth cohort.

Results: The number of sick persons in CHS was approximately constant for 14 years, for all definitions of “sick”. The estimated number of sick persons in the birth cohort was approximately constant from ages 55-75, after which it decreased.

Discussion: The relative excess of older persons who are sick in later life is caused by a decline in the number of healthy persons rather than an increase in the number who are sick. Cohort data that include the number of deaths can detect interesting patterns in aging and health.

#### Disciplines

Biostatistics | Clinical Epidemiology | Disease Modeling | Statistical Models | Vital and Health Statistics

#### Suggested Citation

Diehr, Paula; Derleth, Ann; Newman, Anne; and Cai, Liming, "Is the Number of Sick Persons in a Cohort Constant Over Time?" (October 2005). *UW Biostatistics Working Paper Series.* Working Paper 264.

http://biostats.bepress.com/uwbiostat/paper264

#### Included in

Biostatistics Commons, Clinical Epidemiology Commons, Disease Modeling Commons, Statistical Models Commons, Vital and Health Statistics Commons