So far, all of the procedures covered in this statistical
concepts section of the *Student Resource Website* have
involved estimating population parameters, such as population means
and standard deviations. Such tests are called **parametric
statistics**, and they represent by far the most common
statistical tests used in psychology.

However, there are times when parametric tests are inappropriate.
The most common situation when parametric tests should be avoided is
when the scale of measurement for the variables is either nominal or
ordinal. There are statistical procedures that are used in those
situations that are called **nonparametric statistics**, because
they do not involve estimating population parameters.

We will cover the most commonly used nonparametric procedures in this section and provide references to some of the less commonly used procedures. You can either click on each of these topics in the table of contents below or click on the next page button to move to the next topic.