adding description to read me

README.md

-# ACTG #
+# AIDS Clinical Trial Group (ACTG) Study Dataset #
 
-This package contains data from ACTG.
+The ACTG study 320 compared a combination of three antiretroviral drugs against a pair. 
 
 ### What is this repository for? ###
 
 * Quick summary
 
-### List of Variables ###
+### List of Variables (variable name: definition) ###
 
-* 
+* id: patient identifier
+* male: 1=male, 0=female
+* black: 1=black, 0=non-black
+* hispanic: 1=hispanic, 0=non-hispanic
+* idu: 1=history of injection drug use, 0=no history
+* art: 1=triple therapy, 0=double therapy
+* delta: 1=endpoint (AIDS or death), 0=no endpoint
+* drop: 1=loss to follow up, 0=not
+* r: 1=in subcohort, 0=not
+* age: years of age at randomization
+* karnof: Karnofsky score (100=normal, 0=dead)
+* days: days from randomization to endpoint of censoring
+* cd4: CD4 count in cells/mm^3 at randomization
+* stop: day therapy stopped, missing if not stopped
 
 ### Notes ###
 
-* 
+* There is one record per patient in the dataset.
+* r is a constructed variable to illustrate confounding.