1. Chapter 9 Regression Wisdom
Subsets
If the data consist of two or more groups that have been thrown together, it is usually best to fit different linear models to each group than to try to fit a single model to all the data
Residuals Plot
Extrapolation
It is unsafe to predict values of y for values of x that are far from the ones used to find the linear model equation. Extrapolation in time is particulary dangerous.

2. OUTLIERS x y
x-outiers
y-outliers
Model Outliers y x y x

3. Outliers (cont.) High Leverage Points Influential Points (x-outliers)
High Leverage Points that are model outliers x y y x

4. Project Make sure the relationship is straight.
Check Residuals
Beware of extrapolating
Careful extrapolating into the future.
Check for subsets (different groups)
Look for outliers
Beware of high leverage points and specially of those that are influential.
Consider comparing two regressions
Beware of Lurking Variables and Causation
Watch out when dealing with data from summaries

5. Chapter 10 Re-expressing Data

6. Goals of Re-expression
Make the distribution of a variable more symmetric

7. Goals of Re-expression
Make the spread of several groups more alike

8. Goals of Re-expression
Make the form of a scatterplot more nearly linear.
Goal 4
Make the scatter in a scatterplot spread out evenly rather than following a fan shape