Changes to 2.1 Categorical Variables
Adding a data set for 2.1.
Addition to Chapter 0 from Chapter 2
Changes to 2.2
Minor changes to 2.1 and 2.2, changes to 2.3
Minor changes to 2.1, changes to 2.4
reorganizing sections
changes to 2.5 and 2.6 with sections removed to chapter 0
minor changes to section/subsections
initial heading changes