 Any medical test with 90% sensitivity and 90% specificity (and this was declared as a standard performance of ER and PR test in breast cancer in 2010 by ASCO) will not be expected to result in only 10% of false negative and 10% of false positive results.The expected test errors are subject to effect of prevalence in medical testing.Actual prevalence of ER positive breast cancer is in a range of 80%.