8.5a - Unequal Slopes Model - Minitab

Minitab 18

Minitab®

With new a new data file, Salary-new Data,. When we re-run the program with this new data and find that we get a significant interaction between gender and years.

To do this, open the Minitab dataset Salary-new Data.

Go to Stat > ANOVA > GLM (general linear model) and follow the same sequence of steps as in Lesson 10.4a.

Analysis of Variance
Source DF Adj SS Adj MS F-Value P-Value
years 1 8000.0 8000.0 800.00 0.000
gender 1 65.5 65.45 6.55 0.043
years*gender 1 500.0 500.0 50.00 0.000
Error 6 60.0 10.00    
Total 9 12970.0      

So here we can’t simply remove the interaction term and compare the treatment means at the mean level of the covariate (3 years out of college). The magnitude of the difference between males and females differs (giving rise to the interaction significance).