A study was performed in Basel Switzerland on the relationsh

A study was performed in Basel, Switzerland, on the relationship between the concentration of plasma antioxidant vitamins and cancer risk. Below shows data for                 plasma vitamin-A concentration for stomach cancer cases and controls.
                Stomach-Cancer cases: Mean: 2.65, Standard Error: 0.11, n = 20
                Controls: Mean= 2.88, n= 2421

1) If we assume that the mean plasma vitamin-A concentration among controls is known without error, test whether the true mean concentration is the same for stomach-cancer cases and controls, by reporting a p-value (two-sided).

2) How many stomach-cancer cases are needed to achieve 80% power if the mean plasma vitamin-A concentration among controls is known without error, the true difference in mean concentration is 0.20 ?mol/L, and a two-sided test is used with ? = 5%?

Solution