Difference between Z-test and t-testWatch this thread
The researcher found that 12 of the 31 women had taken the oral contraceptive pill at some time and that 19 had not. He obtained the following results relating to age at menopause, and concluded that taking the pill does not delay menopause:
Pill Users: n=12, mean=47.2, SD=2.1
Non Pill Users: n=19, mean = 47.8, SD=2.1
All i can think of is since n=12 and n=19 - however I thought I would look at the sample size of n=31 and deduce the statistical test from that?