An experiment to test a new gasoline additive, Gasplus, was performed on three different cars: a sports car, a minivan, and a hybrid. Each car was tested with both Gasplus and regular gas on 10 different occasions, and their gas mileage was recorded. Here are the boxplots.

A two-way ANOVA with interaction model was run, and the following ANOVA table resulted.

A plot of the residuals vs. predicted values showed:

What conclusions about the additive and car types do you draw? Do you see any potential problems with the analysis?

Transcribed Image Text:

500 37.5 25.0- 125 24 F 8 Hybrid Mrivan Sports Type Gasplus Reguier Addibve Sum of Mean DF Squares Square F-ratio P-value 2 23175.4 11587.7 2712.2 0.0001 Source Type Additive92.1568 92.1568 21.57 0.0001 Interaction 2 51.8976 25.9488 6.0736 0.0042 Error Total 54 230.711 59 235502 4.27242 宮2.5 S. 2.5 -5.0 12.5 25.0 37.5 50.0 Predicted Values (mp)