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 partial box plots:

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:

50.0 37.5 25.0 - 12.5 32 E 28 24 20 Ct Hybrid Minivan Sports Type Gasplus Regular Additive Sum of Mean Source DF Squas Square F-ratio P-value Type Additive 1 92.1568 92.1568 21.57 <0.0001 Type × 2 51.8976 25.9488 6.0736 0.0042 223175.4 11587.7 2712.2 <0.0001 Additive Error Total 54 230.711 59 23550.2 4.27242 25 2.5 -5.0 12.5 25.0 37.5 50.0 Predicted Values (mpg) キ 丰+丰 (Bdu) senpisau