Question: A variety of sources suggest that individuals assess their health, at least in part, by estimating their percentage of body fat. A widely accepted measure of body fat uses an underwater weighing technique. There are, however, more convenient methods using only a scale and a measuring tape. An article in the Journal of Statistics Education by Roger W. Johnson explored regression models to predict body fat. The file entitled Bodyfat lists a portion of the data presented in the cited article.

1. Create a scatter plot for each explanatory variable with the dependent variable. Are there any obvious transformations needed?
2. Use backward stepwise regression (by hand in Stata or using Stata’s "sw" command) to establish the relationship between body fat and the variables in the specified file. If you need to transform any variables, use the transformed versions in your stepwise analysis.
3. Summarize the model found in part (b) in a sentence, describing the result as clearly as possible.
4. Using the model found in part (b), construct the overall residual diagnostic plot (res vs yhat). Comment on the plot and whether anything looks suspicious.
5. Construct a standardized residual vs yhat plot. Do there appear to be any outliers?
6. Test the residuals to see if they are normally distributed.

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