EXAMPLE 1 Soda consumption

In July 2015, Gallup conducted telephone interviews with a random sample of 1009 adults. The adults were at least 18 years of age and resided either in one of the 50 U.S. states or in the District of Columbia (DC). Survey respondents were asked to consider several different foods and beverages and to indicate if these were things they actively tried to include in their diet, actively tried to avoid in their diet, or didn’t think about at all. Of the 1009 adults surveyed, 616 indicated that they actively tried to avoid drinking regular soda or pop. Based on this information, what can we say about the percentage of all Americans 18 years or age or older who actively try to avoid drinking regular soda or pop?

Our population is adults at least 18 years of age or older who reside in the United States or District of Columbia. The parameter is the proportion who actively tried to avoid drinking regular soda or pop in 2015. Call this unknown parameter p, for “proportion.’’ The statistic that estimates the parameter p is the sample proportion