These data pertain to measures of lung function:  fvc (forced vital capacity), or total lung
capacity measured from maximum inhalation to maximum exhalation, and
fev1, the volume expelled in the first second of the maneuver for fvc.
The former measures lung tissue elasticity, while the latter
measures airway disease.  The data were collected as part of the Six
Cities study, which studies the effects of air pollution in adult and
child populations in six selected U.S. cities.

Potential predictors are listed below. There are one baseline and up to two 
follow-up measures for each participant, although
there are missing data. Missing data are indicated by ``NA''.


id	 participant ID
yos	 year of study (1=initial 4=first follow-up, 7=second follow-up)
fev1	 in liters
fvc      in liters
height	 in meters
weight   in pounds
pack_yrs number of packs times number of years
fume_exp exposure to fumes, in years
dust_exp exposure to dust, in years
age	 in years
cigwk    in packs per week
chstil1  0=no ill 1=bronchitis 2=emphysema 3=1&2 4=pneumonia
	  5=1&4 6=2&4 7=all 3
city	 1=watertown 2=kingston-harriman 4=st.louis 5=steubenville
	  6=portage 9=topeka
sex	 1=male 2=female
smok	 0=never 1=ex 2=current