This chapter contains sections titled: The Purpose of this Chapter An Illustrative Example Five Reasons for Believing that the Simple Carry-over Model is not Useful In Summary: the Case Against Mathematical Approaches to Carry-over Using the Simple Carry-over Model Where to Find Out More about the Simple Carry-over Model Author's note: “Some passages of text are indicated with an asterix (*). This is either because the material is rather more difficult than the general level of the book or because, whatever the theoretical interest, its utility to the analyst is low.”