A poll was conducted by the Gallup organization to find out how Americans' opinions about the U.S Economy have changed recently. Researchers randomly sampled 1726 adults ages 18 and over , living in all 50 states and the district of columbia from june 1st to june 22nd. 1005 of those contacted responded to the poll. Of those , 15%think economic conditions are excellent or good. what is the parameter study?