What is a Manipulated Variable?

Definition: A manipulated variable is an independent variable subject to the changes of an experiment to analyze its effect on a dependent variable. Simply put, the variable is modified to assess its influence over the experiment’s overall result.

What Does Manipulated Variable Mean?

Manipulated variables are frequently used in scientific experiments or theoretical research. This method evaluates the change in the results obtained by modifying a given independent variable’s value. By analyzing these changes the person in charge of the experiment can conclude what’s the degree of influence of this variable over the element or phenomena being studied.

The manipulated variable experiment is designed to understand the cause-effect relationships between the elements being studied, but in order to identify and try out a manipulated variable there has to be a research or an hypothesis that backs the idea that this variable has a correlation with the dependent variable (the one that the experiment is trying to predict or study). Of course, in order for this to work, the person performing the experiment has to be able to control the input of the manipulated variable.

Here’s an example of this experiment.

Example

Mr. Malone is a plant manager at a company that manufactures water bottles in different sizes. He’s currently evaluating the performance of individual production lines and there’s one production line that is underperforming when compared to the quota established for it. Mr. Malone suspects that the reason for this poor performance is the operator assigned to that line. In this scenario, how can Mr. Malone use a manipulated variable experiment to reach a conclusion about the situation?

Our concept of manipulated variable state that the independent valued identified as influential must be changed in order to study the change in the results obtained. According to this concept, what Mr. Malone should do is to replace the worker with perhaps three or four different workers, to see how productivity is affected on each case. If there’s a significant change in the output figures of these new workers vs. the initial worker’s performance, it would mean that the problem is indeed the person that is currently operating the line.