A group of researchers want to conduct a clinical trial to determine whether a new cholesterol-lowering agent is useful in preventing coronary heart disease (CHD). They identified 12,327 potential participants for the trial. Upon initial exam, 309 were found to have CHD. The remaining subjects entered the trial and were divided equally into the treatment and placebo groups. Of those in treatment group, 505 developed CHD after 5 years of follow-up, while 477 developed CHD during the same period in the placebo group. What is the incidence during the 5-year study?