independent variable

1. Mathematics. A variable whose value determines the value of other variables.
2. Statistics. A manipulated variable in an experiment or study whose presence or degree determines the change in the dependent variable.

Advertising research: the independent variable is the element that is subject to arbitrary (not random) change, in order to test the results. For example: If the objective were to test audience response to headline copy, keeping all other factors equal, the sample audience would be subjected to different headline copy to determine the effectiveness of the various headlines. The audience response would be dependent on the stimulus provided-in this case the copy; therefore, the headline copy would be considered the independent variable when it came time to chart the results.

Mathematics and statistics: the factor that is not dependent for change on other factors. For example: if y = 3x, the value of y is always dependent on the value of x, but x can be anything and is therefore the independent variable.

Two or more variables that are in no way associated with or dependent on each other.

One that may take on any value in a relationship; for example, in y = f(x), x is the independent variable. For example, independent variables that influence sales are advertising and price. See also Dependent Variable.

The variable being studied that is manipulated or controlled by an experimenter. In a drug study an investigator may give several doses of a drug (independent variable) to determine the most effective, symptom-reducing (dependent variable) level.

In any study of cause and effect, the independent variable is the causal factor which shapes or determines the dependent variable. For example, an investigation of sediment transport in rivers would identify stream velocity as the independent variable which determines the size of particle that can be transported. In human geography, it is not always as easy to decide which is the independent variable; to some extent, it depends on the theoretical basis of the study, but, as a rule of thumb, the independent variable should predate the dependent variable, and should have a causal effect. In any graph of related variables, the independent variable is plotted on the x-axis.

Variable that is manipulated, sometimes experimentally, in order to observe its effects on a dependent variable. For example, in a study of the effects of age on sports participation, age is the independent variable and sports participation the dependent variable.