In Exercise 11.67 (page 322), we described a Yale University study. Let’s consider a redesign in which researchers randomly assigned 46 participants to place one of three substances 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 unde r the artificial lights used at night. 

a. What are the independent variables and their levels? 

b. What kind of ANOVA would we use?