Question: Cancer of the colon and rectum is common in the Mediterranean region than in other Western countries. The Mediterranean diet contains little animal fat and lots of olive oil. Italian researchers compared 1953 patients with colon or rectal cancer with a control group of 4154 patients admitted to the same hospitals for unrelated reasons. They estimated consumption of various foods from a detailed interview, then divided the patients into three groups according to their consumption of olive oil. Here are some of the data.

a) Is this study an experiment? Explain your answer

b) Is high olive oil consumption more common among patients without cancer than in patients with colon cancer or rectal cancer?

c) Find the chi-square statistic X² What would be the mean of X² if the null hypothesis (no relationship) were true? What does comparing the observed value of X² with this mean suggest? What is the P value? What do you conclude?

d) The investigators report that “less than 4% of cases or controls refused to participate.” Why does this fact strengthen our confidence in the results?