manipulated variable
Definition
Condition or quantity altered (manipulated) to regulate, or initiate a change in, some other condition or quantity. For example, to find out if your weight depends on the amount of calories you consume, you could lower your calories intake (where calories is the manipulated variable) for a period of time and see how your weight changes in response.
News containing the term manipulated variable
http://www.businessdictionary.com/definition/manipulated-variable.html

