repeat.samples=function(population,sample.size,M){
#this function draws M simple random samples from a given
#population of responses.
#all samples have the same size, given in ``sample.size''
	ybars=NULL
	for(i in 1:M){
	resp=sample(population,sample.size)
	ybars[i]=mean(resp)
	}
	return(ybars)
	}