Independent variable
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In an experimental design, the independent variable (also known as predictor or regressor or manipulated variable) is the variable which is manipulated or selected by the experimenter to determine its relationship to an observed phenomenon (the dependent variable). In other words, the experiment will attempt to find evidence that the values of the independent variable determine the values of the dependent variable (which is what is being measured). The independent variable can be changed as required, and its values do not represent a problem requiring explanation in an analysis, but are taken simply as given.
More generally, the independent variable is the thing that someone actively controls/changes; while the dependent variable is the thing that changes as a result. In other words, the independent variable is the “presumed cause,” while dependent variable is the “presumed effect” of the independent variable.
The independent variable is also called the manipulated variable, predictor variable, exposure variable, explanatory variable, or x-variable. Independent variable is the most common name given for this item.
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[edit] Scientific usage
When observing a physical process, the independent variable is adjusted or allowed to change by the scientist, in order to measure the response of the dependent variable . Often the independent variable is time, which is allowed to change, or a physical quantity (such as voltage, force or frequency) that can be accurately adjusted. To visualize the effect of the independent variable on the dependent variable, a line chart is commonly used. This effect is also called the “response” or the “relation."
[edit] Mathematics usage
When graphing a set of collected data, the independent variable is graphed on the x-axis (see Cartesian coordinates). In mathematics, in functional analysis, it was traditional to define the set of independent variables as the only set of variables in a given context which could be altered. For, even though any function defines a bilateral relation between variables, and it’s even true that two variables might be connected by an implicit equation (for instance, cf. the definition of a circle, x2 + y2 = R2), when computing derivatives it is nonetheless necessary to take a group of variables as “independent,” or else the derivative has no meaning.
[edit] Advertising Usage
An independent variable is what you know about the customer, or what you can observe.
[edit] Examples
In a study of how different dosages of a drug are related to the severity of symptoms of a disease, a researcher could compare the frequency and intensity of varying symptoms (the dependent variables) when varying dosages (the independent variable) are administered, and attempt to draw a conclusion.
In measuring the acceleration of a vehicle, time is usually the independent variable and speed is the dependent variable. This is because when taking measurements, times are usually predetermined, and the resulting speed of the vehicle is recorded at those times. As far as the experiment is concerned, the speed is dependent on the time. Since the decision is made to measure the speed at certain times, time is the independent variable.
