- The population mean of within strata defined by the 's
follows a linear and additive pattern, i.e.

This will be referred to as the*regression equation*.Note: In the following we will use as shorthand for the set of variables, so we can right for the left hand side in the above. I'll also use the term -strata to describe strata determined by a particular set of values .

- The standard deviation of within particular -strata, , is constant over all values of . We'll simplify notation by calling this value .
- The distribution of within -strata is normal.

Rollin Brant 2004-03-24