# Exercise: Multiple regression of muscle strength on age and height

The file strength.sav contains the quadriceps muscle strength data for alcoholic men analysed in the lectures for Weeks 9 and 10.

In this exercise we shall continue the analysis of the measurements of quadriceps muscle strength, height and age. In the exercise Muscle strength, age and height for alcoholic men, Week 9, we saw that muscle strength was significantly positively correlated with height and negatively correlated with age. We also saw that height was negatively correlated with age. In this exercise we examine how height and age together predict muscle strength.

## Questions

1. Carry out multiple linear regression of strength on height and age. What is the equation and what can we conclude?

2. Calculate confidence intervals for the regression coefficients.

3. Carry out graphical checks of the assumptions that the residuals follow a Normal distribution with uniform variance.

4. Create a new variable to represent an interaction between age and height in their effects on strength. Add the interaction term to the regression.

5. Try fitting a curvilinear regression using height only as a predictor. Does there appear to be evidence of a curve rather than a straight line relationship?