The Slope
Rate my professor. Many college courses conclude by giving students the opportunity to evaluate the course and the instructor anonymously. However, the use of these student evaluations as an indicator of course quality and teaching effectiveness is often criticized because these measures may reflect the influence of non-teaching related characteristics, such as the physical appearance of the instructor. Researchers at University of Texas, Austin collected data on teaching evaluation score (higher score means better) and standardized beauty score (a score of 0 means average, negative score means below average, and a positive score means above average) for a sample of 463 professors.21 The scatterplot below shows the relationship between these variables, and regression output is provided for predicting teaching evaluation score from beauty score.
Estimate Std. Error t value Pr(>|t|) (Intercept) 4.010 0.0255 157.21 0.0000
beauty Cell 1 0.0322 4.13 0.0000
(a) Given that the average standardized beauty score is -0.0883 and average teaching evaluation score is 3.9983, calculate the slope. Alternatively, the slope may be computed using just the information provided in the model summary table.
(b) Do these data provide convincing evidence that the slope of the relationship between teaching evaluation and beauty is positive? Explain your reasoning.
(c) List the conditions required for linear regression and check if each one is satisfied for this model based on the following diagnostic plots.
Beauty Teaching evaluation
−1 0 1 2 2 3 4 5
Beauty Residuals
−1 0 1 2 −1 0 1
Residuals
−2 −1 0 1 2
0 50 100 150
Order of data collection Residuals
0 100 200 300 400
− 1 0 1
