Scientists are interested in various predictors of HDL (the so-
called good cholesterol).  In particular, they are interested in 
predictive capability of the presence of a substance called sinking 
pre-beta.

    The file prebeta.sas7bdat contains
    HDLC     HDL cholesterol   (mg/dl)
    TOTC     total cholesterol (mg/dl)
    TRIG     tirglyceride      (mg/dl)
    PREBETA  pre-beta (0=absent/1=present)


    Answer the following questions.  Be prepared to back up your 
assertions with the appropriate analyses.
    
    Are TOTC, TRIG, PREBETA alone (that is, individually) predictive 
of HDL?
    Are TOTC, TRIG, and PREBETA together predictive of HDL?
    Do the three possbile two-variable interactions between the 
predictors provide additional predictive capability?
    Is there evidence of confounding between X1, X2, X3?
    Research Question 1:  Does the predictive capability of TOTC and 
TRIG change according to whether a person has sinking prebeta?
    Research Question 2:  Does pre-beta itself help predict HDL?