IDENTIFICATION OF VARIABLES
OVERVIEW:
In order for any experiment to be a fair test of the hypothesis, it is essential to
establish a clear understanding of the relationship between all of the factors that
potentially impact the results of the experiment. Variables can be classified as
independent, dependent, or controlled (control). The Identification of Variable
section helps to assure that the experiment is a fair test of the hypothesis by first
identifying the independent and dependent variables, In addition, it identifies all
the potential control variables along with prescribing a mechanism for controlling
them.
INDEPENDENT VARIABLE:
The independent variable is the element that will be intentionally changed by the
researcher during the experiment. It often reflects the “cause” element in the
hypothesis statement. Therefore, it is anticipated that a change in the
independent variable will result in a measurable or observable change in the
dependent variable.
Sample Independent Variable:
In the hypothesis “If the pH of potting soil increases then the growth rate of
tomato plant will increase proportionally,” the independent variable is the
pH of the potting soil. This is the variable that the experimenter will be
intentionally changing in the experiment to determine if it impacts the
growth of the tomato plant.
There should only be one independent variable tested in an experiment.
Otherwise, it is difficult to determine the impact that each of the independent
variables has on the dependent variable.
DEPENDENT VARIABLE:
The dependent variable is the element that will exhibit an observable or
measurable change as a direct result of any change in the independent variable.
It has If often reflects the “effect” element in the hypothesis statement. It is
possible to have more than one dependent variable since manipulating the
independent variable can influence different things.
Sample Dependent Variable:
In the hypothesis “If the pH of potting soil increases then the growth rate of
tomato plant will increase proportionally,” the dependent variable is the
growth rate of the tomato plant. This is the variable that is anticipated to
change as a result of the change in the independent variable (the pH of
the soil).
CONTROL VARIABLES:
There are often other factors, other than the independent variable, that cause
changes to the dependent variable. In order to fairly test the hypothesis, these
other factors need to be identified and kept constant (the same) for all test
samples. By controlling these conditions, it can be assured that the independent
variable is the only element that could create change in the dependent variable.
Sample Control Variables:
In the hypothesis “If the pH of potting soil increases then the growth rate of
tomato plant will increase proportionally,” it is possible that factors might
impact the growth rate of the plant other than the pH of the soil. Some
possibilities might include temperature, the amount of available moisture
(watering), and the number of hours the plant is exposed to light each day.
The experiment should provide for the control of these variables so that
these conditions are the same from test subject to test subject.