Cocaine addiction is hard to break. Addicts need cocaine to feel any pleasure, so perhaps giving them an antidepressant drug will help. An experiment assigned chronic cocaine users to take either an antidepressant drug called desipramine, lithium, or a placebo. Lithium is a standard drug to treat cocaine addiction. A placebo is a dummy drug, used so that the effect of being in the study but not taking any drug can be seen. Here are the results after three years. Treatment Cocaine relapse
Yes No
Desipramine 10 14
Lithium 18 6
Placebo 20 4

a. If cocaine relapse is independent of which treatment a cocaine user has received, how many cocaine users taking the desipramine would be expected to experience relapse?
b. Do cocaine addicts taking the desipramine, lithium, and placebo have different rate of relapse? Perform a hypothesis test using α = 0.01.