A randomized, double-blind, clinical trial was conducted on patients who had coronary angioplasty to compare the drug lovastatin to a placebo. The percentage of stenosis (narrowing of the blood vessels) following angioplasty was measured on 160 patients given lovastatin and on 161 patients given the placebo. For the lovastatin group the average was 46%, with an SD of 20%. For the placebo group the average was 44%, with an SD of 21 %. What type of analysis is appropriate for these data?