data respire;
   input air $ exposure $ smoking $ level count @@;
   datalines;  
low no non   1 158 low  no  non 2   9    
low no ex    1 167 low  no  ex  2  19   
low no cur   1 307 low  no  cur 2 102  
low yes non  1  26 low  yes non 2   5    
low yes ex   1  38 low  yes ex  2  12   
low yes cur  1  94 low  yes cur 2  48   
high no non  1  94 high no  non  2  7    
high no ex   1  67 high no  ex   2  8   
high no cur  1 184 high no  cur  2 65  
high yes non 1  32 high yes non 2   3    
high yes ex  1  39 high yes ex  2  11   
high yes cur 1  77 high yes cur 2  48  
low  no  non 3  5  low  no non  4  0
low  no  ex  3  5  low  no ex   4  3
low  no  cur 3 83  low  no cur  4 68
low  yes non 3  5  low  yes non 4  1
low  yes ex  3  4  low  yes ex  4  4
low  yes cur 3 46  low  yes cur 4 60
high no  non 3  5  high no  non 4  1
high no  ex  3  4  high no  ex  4  3
high no  cur 3 33  high no  cur 4 36
high yes non 3  6  high yes non 4  1
high yes ex  3  4  high yes ex  4  2
high yes cur 3 39  high yes cur 4 51
;run;