Explanatory variable

The extent of a relationship between two quantitative variables is what statisticians are looking for in a correlation. Is one variable influencing the other? If so, the influencing variable is called the explanatory variable because it explains what is happening to the other variable. The variable that is being influenced is called the response variable because it is simply responding to the explanatory variable. Their names define their roles in a correlation.

Explanatory variables also go by the name of independent variables, factors, predictors, causes, and other names that mean roughly the same as "controller variable".

Response variables also go by the name of dependent variables, outcomes, effects, and other names that mean roughly the same as "controlled variable".

Examples: Which is the explanatory variable and which is the response variable?

Q 1) The temperature of a pot of tea compared to the height of the flame underneath the teapot

A 1) The height of the flame is the explanatory variable because it explains the temperature of the tea, which is the response variable.

Q 2) The number of hours worked compared to your paycheck

A 2) The number of hours worked is the explanatory variable because it explains how large (or small) your paycheck is, which is the response variable.

*Note: Researchers must be careful when trying to prove causality through a correlation because there may be another unseen force at work that is affecting both the explanatory and the response variables. This unseen force is called a "lurking" variable because it lurks in the shadows (insert spooky laugh here). A lurking variable can also be referred to a "confounding" variable.

Q 3) The number of umbrellas sold compared to how many bottles of flu medicine sold.

A 3) Is the explanatory variable the number of umbrellas sold? If this were true, then the response variable would be the number of bottles of flu medicine sold. You are stating that umbrella purchases cause people to buy flu medicine. Or is it the other way around: do flu medicine sales cause umbrella sales? This is crazy talk!

What is truly going on in example 3 is that there is a lurking variable that is influencing both of the other variables. The lurking variable in this problem is probably the inclement weather that winter brings... brrrrrrrrr!