statistics, confidence interval, hypothesis testing

Example: The herb ginkgo biloba is commonly used as a treatment to prevent dementia. In a study of effectiveness of this treatment, 1545 elderly subjects were given ginkgo and 1524 elderly were given placebo. Among those in the gingko treatment group, 246 later developed dementia, and among those in the placebo group, 277 later developed dementia (based on data from the Journal of the American Medical Association). We want to use a 0.01 significance level to test the claim that ginkgo is effective in preventing dementia.