Responding variable is a variable whose value depends on the changes made by the researcher in the course of the experiment. The responding variable is also called the dependent variable and the factor on which it depends is called the independent variable or the manipulated variable.
We call the dependent variable to be the responding variable because it “responds” to changes in the manipulated variable. The manipulated variable is controlled (“manipulated”) by the researcher and hence is called the manipulated variable.
Some examples of responding variables:
- Suppose that a researcher wishes to study the effects of four different fertilizers on the growth rate of crops. Here the growth rate of the crops is the responding variable because it depends on the kind of fertilizer chosen by the researcher. The kind of fertilizer chosen is the manipulated variable.
- A person goes on a diet to lose weight. Here the magnitude of weight loss is the response variable because it depends on the diet of the person. The diet of the person can be changed and is the manipulated variable.
- A person’s heart rate increases during periods of physical activity. Here the heart rate is the responding variable which increases when a person is physically active. The amount of physical activity is the manipulated variable as it is under the control of the individual.
How can we study and predict the responding variable?
We can study how the responding variable depends on the cause by plotting them on a graph and constructing a scatterplot as shown below:
As seen in the picture above, we can construct a “best fit” line which gives us a linear relationship between the dependent and the independent variable. The equation of the best fit line can be found by performing linear regression.