Naming of dependent and independent variables in simple linear regression I'm currently doing some self-study on Simple Linear Regression. I came across the terms "dependent variable" (eg. Sales volume) and "independent variable" (eg. Advertising budget). 
I am curious to learn why is it called dependent and independent variable. I know what these variables does,but just have no clue why they are called as such.
 A: From Statistics.com we have a fairly informative definition of the two which hopefully provides you with some justification for the choice of the terms.

Statistical models normally specify how one set of variables, called dependent variables, functionally depend on another set of variables, called independent variables. While analysts typically specify variables in a model to reflect their understanding or theory of "what causes what," setting up a model in this way, and validating it through various metrics, does not, by itself, confirm causality. The term "(in)dependent" reflects only the functional relationship between variables within a model.

So dependent variables are dependent because we specify how they functionally depend on another set of variables
This government website provides some additional intuition. 

An independent variable is exactly what it sounds like. It is a variable that stands alone and isn't changed by the other variables you are trying to measure. For example, someone's age might be an independent variable. Other factors (such as what they eat, how much they go to school, how much television they watch) aren't going to change a person's age.

I think this idea that the independent variables should not be changed by the other variables you are trying to measure is reflected in the underlying assumptions of regression:

The predictors [independent variables] are linearly independent, i.e. it is not possible to express any predictor as a linear combination of the others.

If we go to Dictionary.com, it says that the terms came into use between 1850-55, and provides a boiler plate definition which also provides some 
