The cd4 data frame is made by a total of 2376 rows and 8 columns providing information on CD4 cell counts of 369 subjects followed for a maximum of 12 measurement occasions.
data(cd4)
A data frame with 2376 observations on the following 8 variables:
sbj.id
subject id
time.id
time id
count
CD4 count
lcount
log(CD4 count + 1)
time
years since seroconversion
age
age (yrs) centered around 30
packs
packs of cigarettes per day
partners
number of sexual partners
drugs
recreational drug use indicator
cesd
depression score
Multi-center AIDS Cohort Study providing a total of 2376 CD4+ cell counts of 369 HIV-infected men covering a period of approximately eight and half years. The number of measurements for each individual varies from 1 to 12. The CD4+ cell data are highly unbalanced.
Zeger, Scott L., and Peter J. Diggle. "Semiparametric models for longitudinal data with application to CD4 cell numbers in HIV seroconverters." Biometrics (1994): 689-699.