A group of individuals is randomized in a double-blind fashion to 
receive daily either 200 IU of vitamin E or placebo for 1 year.  
Serology is performed at the beginning and end of the study to measure 
titres of various viral antibodies.  A notation is made whether any of 
the titres increased four-fold from baseline to the end of the study.  
The file virus.txt contains 

    TREATment (E/P), and (0/1) indicator variables for RSV, Flu A, Flu 
B, Human metapneumovirus (hmpv) coronavirus OC43 and coronavirus 229E, 
Parainfluenza, (PIV)1/3, and PIV-2, where 1 indicates a four-fold 
increase or more and 0 indicates anything less.

    Is vitamin E protective against these viruses?

    After seeing reports of the way zinc has become the latest "cold 
cure", the investigator looks to see whether zinc status might be 
predictive of whether a subject experienced these viruses.  The 
variable zn_low is 1 if a subject's mean zinc levels were less than 70 
ug/dL or 0, otherwise.  Is zinc protective against these viruses?