The following statements are wrong but can be corrected by substituting one word or phrase. Identify the incorrect word or phrase in each of the following statements and supply the correct word. 

a. A researcher examined the effect of the ordinal variable “gender” on the scale variable “hours of reality television watched per week.”

b. A psychologist used a between-groups design to study the effects of an independent variable (a workout video) on the dependent variable (the weight) of a group of undergraduate students before and after viewing the video. 

c. In a study on the effects of the confounding variable of noise level on the dependent variable of memory, researchers were concerned that the memory measure was not valid. 

d. A researcher studied a population of 20 rats to determine whether changes in exposure to light would lead to changes in the dependent variable of amount of sleep.