MACS-cd4-vload0.txt

      Multicenter Aids Cohort Data on CD4 and HIV viral load
      ------------------------------------------------------

Introduction:
-------------

This data set contains repeated measures on n=307 subjects that
are infected with HIV, the virus that causes AIDS.  The data
contains measurements of CD4 cells, an immunologic marker of
the impact of HIV infection, taken at approximately semi-annual
follow-up visits.  Also included is a measurement of CD8 cells
which are another type of blood cell.  

The data contains measurements obtained in 
the first 4 years after infection and excludes subjects that
died within the first 4 years. 

There are several variables that give time information.  First,
the variable MONTHS measures the number of months since infection.
The variable VTIME is the number of calendar months since January
1984, ATIME is the calendar time (months since 1/1984) at which
a subject is diagnosed with AIDS, the disease caused by HIV infection.
Note that although at MONTHS=0 a subject is infected with HIV,
there may be a long delay until the serious consequences of disease 
manifest -- this latter time being the time of AIDS diagnosis.
The variable ATIME is missing if a subject was not observed to 
be diagnosed with AIDS. Finally, DTIME is the calendar time 
of death (months since 1/1984) or follow-up time depending on the
value of IDEATH.

Some subjects miss scheduled visits or choose to discontinue study 
participation and thus have fewer that the expected number of 
measurements.


Variables: (columns of the data file)
----------
  ID = subject ID 
  MONTHS = months since seroconversion (detection of infection)
  AGE = age of subject
  CD4-COUNT = # of CD4 positive cells (helper cells) per mm^3
  CD8-COUNT = # of CD8 positive cells (supressor cells) per mm^3
  VLOAD0 = viral load at baseline (copies per ml)
  AIDSCASE = 1 if no AIDS observed; 2 if AIDS observed; 3 if died prior to AIDS
  VTIME = calendar time of study visit in months since January 1984
  SCTIME = calendar time of seroconversion (infection) in months since 1/1984
  ATIME = calendar time of AIDS diagnosis in months since 1/1984
  DTIME = calendar time of death in months since 1/1984, or follow-up time
  IDEATH = indicator of death at DTIME (1=death, 0=censored)

Note:  ATIME is missing (NA) if the time was not observed during
       study follow-up (ie. subjects remained AIDS free and alive). 

Note:  There is a lower limit of detection for viral load and thus 
       measurements at 300 reflect this detection limit.

Note:  The ability to measure viral loads actually became available many
       years after the study was started, and for many subjects this 
       measurement needed to obtained from stored samples.  Thus, not 
       all subjects have a viral load at baseline (perhaps due to limited 
       blood samples).