Hi critical values for a two tailed test with a=0.02 z<-2.575 z >+2.575 a a/2 crtical regions 90% 0.1 5% z <-1.645 z >+1.645 95% 0.05 2.50% z <-1.96 z >+1.96 98% 0.02 1% z <-2.33 z >+2.33 99% 0.01 0.50% z<-2.575 z >+2.575