Editing Interaction (statistics) (section)

===Categorical variables===
Sometimes the interacting variables are categorical variables rather than real numbers and the study might then be dealt with as an [[analysis of variance]] problem.  For example, members of a population may be classified by religion and by occupation.  If one wishes to predict a person's height based only on the person's religion and occupation, a simple ''additive'' model, i.e., a model without interaction, would add to an overall average height an adjustment for a particular religion and another for a particular occupation.  A model with interaction, unlike an [[additive model]], could add a further adjustment for the "interaction" between that religion and that occupation.  This example may cause one to suspect that the word ''interaction'' is something of a misnomer.

Statistically, the presence of an interaction between categorical variables is generally tested using a form of [[analysis of variance]] (ANOVA). If one or more of the variables is continuous in nature, however, it would typically be tested using moderated multiple regression.<ref name=Overton2001>{{Cite journal
 | author = Overton, R. C.
 | year = 2001
 | title = Moderated multiple regression for interactions involving categorical variables: a statistical control for heterogeneous variance across two groups
 | journal = Psychol Methods
 | volume = 6
 | issue = 3
 | pages = 218–33
 | doi = 10.1037/1082-989X.6.3.218
 | pmid = 11570229
 }}</ref> This is so-called because a moderator is a variable that affects the strength of a relationship between two other variables.