ztest1<-function(xbar,stdev,n,mu=0,alpha=.05,alt='two.sided')
{
sem<-stdev/sqrt(n)
zbar<-(xbar-mu)/sem
zval<-ifelse(alt=='two.sided',qnorm(1-alpha/2),qnorm(1-alpha))
lcl<-ifelse(alt=='less',-1/0,xbar-zval*sem)
ucl<-ifelse(alt=='greater',1/0,xbar+zval*sem)
pvalue<-switch(alt,two.sided=ifelse(xbar>mu,2*(1-pnorm(zbar)),2*pnorm(zbar)),
        greater=(1-pnorm(zbar)),less=(pnorm(zbar)))
cbind(xbar,sem,lcl,ucl,pvalue)
}