data(byssinosis)| [,1] | dust | 
| Factor w/ 3 levels "most","less" | [,2] | 
| race | Factor w/ 2 levels "white","non-white" | 
| [,3] | sex | 
| Factor w/ 2 levels "male","female" | [,4] | 
| smok | Factor w/ 2 levels "smoker","non" | 
| [,5] | emp | 
| Factor w/ 3 levels "<10","10-20",...< td=""> | [,6]10","10-20",...<> | 
| yes | int, Number of workers who suffered byssinosis |