Randomized controlled trials (RCTs) are generally regarded as the gold standard in assessing treatments. There are some good reasons for this, but there is also some tarnish on the gold standard. Read more!

We very often set the cutoff for a significant p value at 0.05, and minimal acceptable power at 0.8. Sometimes p of 0.01 is demanded. Sometimes power of 0.90 is demanded. But what are these values and how are they chosen? Read more!

Two terms that are frequently confused are *moderation* and *mediation*:

**Definitions of moderating and mediating:**

A mediating variable is one that accounts for or alters another relationship. A strict definition is that the mediating variable has to greatly reduce or even eliminate the relationship. A more lenient definition is that it affects the relationship. I favor that more lenient definition. A *moderating* variable is one that *interacts* with a variable. An *interaction *means that the relationship between one independent variable (IV) and the dependent variable (DV) is different at different levels of the *other *IV. Read more!

In regression and ANOVA, an *interaction* occurs when the effect of one independent variable on the dependent variable is different at different levels of another independent variable. When one or both of the independent variables is categorical, then two common strategies for dealing with interactions are stratifying and adding an interaction term. A somewhat less common method is classification and regression trees. Each has its advantages and disadvantages.

If you often have regression problems in which you have a great many independent variables, partial least squares is a technique you should know about.

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