Notes for this mind map

DV - dependent variable (sometimes referred to as outcome variable)
IV - independent variable (sometimes related to as predictor; for example, treatment name)

Types of variables

Categorical. These variables can take on one of a limited, and usually fixed, number of possible values (gender, hair color etc.). Values of categorical variables cannot be ordered.
Ordinal. Ordinal variables have fixed numbers of values too, however, the important difference is that these values have an order. Rating scales such as Likert scale (limited with five answers from 1 to 5) are the typical examples. The limitation of an Ordinal variable is that degree of difference between the values cannot be adequately measured. For example, levels of treatment satisfaction (Not satisfied, Somewhat satisfied, Very satisfied) can be ordered, but the magnitude of the difference is unknown.
Interval. Interval variables are similar to the Ordinal variables, but also a degree of difference can be calculated too. Such variables can be an integer (duration of treatment in days) or continuous (temperature).

Statistical Test Selection