Each of the following studies examines the relationship between the quality of breakfast and academic performance for third-grade children. Identify which is correlational, which is experimental, and which is nonexperimental.
Study 1: A researcher obtains a sample of 100 third-grade children. Each child is interviewed to determine his typical breakfast, and the child is assigned a score describing the nutritional value of his breakfast. Also, the child's level of academic performance is obtained from school records. The results show that higher academic performance tends to be associated with a higher level of breakfast nutrition.
Study 2: A researcher obtains a sample of 100 third-grade children. The children are randomly assigned to two groups. On arriving at school each morning, one group is given a nutritious breakfast and the other group is given a breakfast relatively low in nutritional value. After 6 weeks, each child's level of academic performance is measured. On average, the children in the nutritious breakfast group had a higher level of academic performance than the children in the low-nutrition group.
Study 3: A researcher obtains a sample of 100 third-grade children. Based on school records, the children are divided into two groups corresponding to high and low academic performance. The children are then interviewed and each child is given a score describing the nutritional value of her typical breakfast. On average, the children in the high academic performance group ate a more nutritious breakfast than the children in the low academic performance group.