The table shows data from a study on the relationship betwee

The

table shows data from a study on the relationship between plasma vitamin A concentration (µmol/L) and stomach cancer.

How many stomach cancer cases are needed to achieve 80% power if the true difference in mean concentration is 0.20 (µmol/L) and a two-sided test is used at a .05 level of significance

Solution

ans) ES = ( mean difference of the sample- true mean difference) / 0.11 = (0.23 - 0.20 ) / 0.11 = 0.2727273...

n =required sample size = [( z-score ( 97.5%) + z-score ( 80%) ) / 0.2727273] ^2
=  [ ( 1.96 + 0.84) / 0.2727273 ]^2 = 105.4045...

n= 106..106 stomach cancer cases are needed to achieve 80% power..