Ciagarette smokers smoke cigarettes differently; some inhale
completely, others only partially, some draw a great deal of smoke
into the mouth while others do not, some only smoke part of a
cigarette, some inhibit a filter's performance by blocking it's
ventilation holes with the fingers, etc. Each such tendency alters
the pharmacological effect of the cigarette on the smoker. Person to
person differences in smoking habits can be measured by blood
levels of nicotine (BPNL, for blood plasma nicotine level) and
carboxyhaemoglobin (COHb, indicating the amount of carbon monoxide
absorbed by the bloodstream) and by the total volume of puffed
smoke (TVPS). These three measurements are likely correlated.

In addition, cigarettes themselves differ by brand and by
type. Three measurements are thought to characterize the potential
for pharmacological effect for a particular cigarette brand and
type: tar yield (TarY), nicotine yield (NicY), and carbon monoxide
yield (COY). These measurements are made by having a machine smoke
the cigarette and retain the smoke for analysis.

55 volunteers were studied in detail during and immediately after
smoking one cigarette of their usual brand and type. A blood sample
was taken 2 minutes after completion of smoking. A cigarette of
identical brand and type was taken for analysis of TarY, NicY, and
COY. Interest lies in examining gender and age differences in
smoking habits (as measured by COHb, BPNL, and TVPS) after adjusting
for the cigarette brand and type (as measured by TarY, NicY, and
COY). Age here is given in decade groups, so that a value of two
corresponds to a subject in his/her twenties, etc. Gender is coded
as 1 for male and 2 for female. The researchers believe that the
covariates may act upon the response variables in a multiplicative
not an additive way. Unfortunately, the data source does not
indicate what the units of measurement are for any of the variables.

Data source: Hand and Taylor (1987). Multivariate Analysis of 
Variance and Repeated Measures. London: Chapman and Hall, Inc.