Each of the following studies examines the relationship between sugar consumption and activity level for preschool children. Identify which is correlational, which is experimental, and which is non-experimental.
Study 1: A researcher obtains a sample of 100 preschool children. Each child’s parents are interviewed to determine the child’s typical diet, and the child is assigned a score describing the amount of sugar consumed daily. Also, the child’s activity level is obtained from direct observation on the playground. The results show that higher sugar consumption tends to be associated with a higher level of activity.
Study 2: A researcher obtains a sample of 100 preschool children. The children are randomly assigned to two groups. On arriving at school each morning, one group is given a high-sugar breakfast, and the other group is given a breakfast relatively low in sugar. After 1 week, each child’s activity level is measured by direct observation on the playground. On average, the children in the high-sugar breakfast group had a higher level of activity than the children in the low-sugar group.
Study 3: A researcher obtains a sample of 100 preschool children. Based on interviews with the parents, the children are divided into two groups corresponding to high-sugar and low-sugar diets. The children are then observed on the playground to obtain an activity-level score for each child. On average, the children in the high-sugar group had higher activity scores than the children in the low-sugar group.