1. Psychology 202a Advanced Psychological Statistics September 15, 2015

2. The plan for today Descriptive statistic for kurtosis. Linear transformations (cont.). Models. Conditional distributions.

3. Numerical assessment of kurtosis fourth moment: bad idea except in very large data sets

4. Changes in mean and sd under linear transformation Linear transformation: Y = a + bX New mean = a + b(old mean)‏ New sd = b(old sd)‏ Special case: the Z score Income example Nonlinear transformations

5. Models What is a model? Example: estimating lumber yield Why are models useful? –Models allow us to clarify what interests us. –Confining our attention to those interests helps us see structure. –But danger lurks in those details that we ignore.