Aresearcher conducts a survey examining eating and sleeping behavior as well as academic performance for a group of elementary school children. the results of the survey indicate that the children who eat a more nutritious breakfast tend to have better grades than the children who have a breakfast low in nutrition. however, the research suspects that the children’s parents may be responsible for this relationship. specifically, the better-educated parents probably encourage their children to eat better food and work harder in school compared to parents with less education. if the researcher is correct, this is an example of the