Kids are often told that they should not crack their knuckles, because otherwise all sorts of terrible things may befall them. It is commonly believed that knuckle cracking leads to arthritis, which de Weber et al. (2011) recently tested in a case-control study. Of 135 patients with osteoarthritis (cases), 24 had frequently cracked their knuckles. Of 80 control patients without osteoarthritis, 19 had frequently cracked their knuckles.

a. What type of graph is ideal for displaying these results?

b. What is the odds ratio for osteoarthritis, comparing knucklecrackers to non-crackers?

c. Give a 95% confidence interval for this odds ratio.

d. Carry out a formal hypothesis test of whether knuckle cracking is associated with osteoarthritis.