/*  
	Set the random seed so we get the same random subsets
												*/
set seed 200
/*  
	Generate random number between 0/1 and put in "u"
												*/
capture gen u=uniform()
/*  
	Create 10 equal size groups based on u
	If it already exists, do nothing
												*/
capture xtile cat=u, nq(10)
/*  
	Create variable pred and make it missing.
	It will hold the predictions
	
												*/
capture gen pred=.
/*  
	Cycle through numbers 1 to 10
	Fit the logistic regression model for 90% of data
	Save predictions.
	Hold result for 10% of data not used for model
												*/
forvalues k=1(1)10 {
quietly logistic death <yoursetofpredictors>  if cat!=`k' 
quietly predict out`k'
quietly replace pred=out`k' if cat==`k'
}
/* 
	Examine the area under the ROC curve
												*/
roctab death pred
/* 
	Housekeeping to reset variables so the do file
	can be re-run
	
												*/
capture replace pred=.
capture drop out*