In statistics, it is important to pay very close attention to language. The following statements are wrong but can be corrected by substituting one word or phrase.

For example, the sentence “Only correlational studies can tell us something about causality” could be corrected by changing “correlational studies” to “experiments.” Identify the incorrect word or phrase in each of the following statements, and supply the correct word.

a. In a study on exam preparation, every participant had an equal chance of being told he/she had to study alone or being told he/she would study with a group. This was a correlational study.

b. A psychologist was interested in studying the effects of the dependent variable of caffeine on hours of sleep, and he used a scale measure for sleep.

c. A university assessed the reliability of a commonly used scale—a mathematics placement test—to determine if it was truly measuring math ability.

d. In a within-groups experiment on calcium and osteoporosis, participants were assigned to one of two levels of the independent variable: no change in diet or calcium supplement.