From 2005 to 2015, an intensive antismoking campaign has been sponsored by the U.S federal government. Suppose in both years, the American Cancer Society randomly and independently sampled 2,000 adults. In 2005, they discovered 418 of the 2,000 sampled defined themselves as smokers. In 2015, they discovered 302 of the 2,000 sampled defined themselves as smokers. Define the population parameter in context in one sentence.