A study was conducted to test if a new drug was effective in reducing the number of headaches. Two groups were formed from a sample with a history of chronice headaches. One group was given the new drug and the other was given a placebo. Of the 30 people that were given the new drug, 20 of them reported relief from their headache. Of the 50 people given the placebo, 25 of them reported relief from their headache. Calculate a 95% confidence interval for the difference in the proportion of subjects reporting relief from their headaches between the new drug and placebo groups.