A reseаrcher wаnts tо study the effect оf regulаr exercise оn cholesterol levels. To do so, he compares the cholesterol levels of two groups. The first group consists of 50 people from a local gym who reported that they exercise regularly. The second group consists of 50 people from the surrounding community who reported that they did not exercise regularly. The cholesterol levels of the members of the gym were substantially lower. The researcher can correctly conclude that ...