In Exercise 13.25, we described a study conducted at Yale University in which researchers randomly assigned 46 participants to place one of three sub stances below their eyes: black grease, black antiglare stickers, or petroleum jelly. They assessed eye glare using a contrast chart that gives a value for each participant, a scale measure. Black grease led to a reduction in glare compared with the two other conditions, antiglare stickers or petroleum jelly (DeBroff & Pahk, 2003). Imagine that every participant was tested twice, once in broad daylight and again under the artificial lights used at night.

a. What are the independent variables and their levels?

b. What kind of ANOVA would we use?