A science fair project experiment often requires a control and variables which are compared to the control subject or group of subjects. The variables are the subject or group of subjects that are changed by the experiment. Variables may also be factors which vary between the control and experimental groups.
For example, if you were conducting an experiment to measure the effect of wind on plants, you could use 12 plants of the same size, 6 in a control group and 6 in the experimental group. You plan to expose the experimental group to wind for specific periods of time. The control group is not exposed to wind. In this experiment, the height of each plant could be a variable, the temperature, and speed of the wind would be other variables.
Variables produce change, whether intentional or not, and affect your results. Variables can even cause the experiment to fail. Identifying all of the variables in an experiment is the key to managing them. In order to keep the variables from influencing the outcome of the experiment, you must also try to keep the conditions for the control and the test group as identical as possible.
When this isn’t possible, you can repeat the experiment several times, or have multiple subjects in both the control and test groups. By averaging the results of the experiment, you might be able to lessen the effects of the variables.
To determine what variables might influence your experiment, ask yourself:
What factors or conditions might affect or ruin the experiment? How might these factors or conditions affect the experiment? What factors or conditions are you changing on purpose?
Variables can be qualitative or quantitative. Quantitative variables are always expressed in numbers while qualitative variables describe the differences in items when the difference is not a measurement. For example, if the wind is a variable in your experiment, the speed in miles per hour is a quantitative variable, while reporting the wind as intermittent or constant would be a qualitative variable. In the example, the height of the plants, the degree of any leaning would be other quantitative variables. Any changes in the color of the plants would be qualitative variables.
Scientists tend to consider quantitative variables more reliable because they can be measured while qualitative variables result from observation, rather than measurement. Identifying and accounting for variables in the experiment and the results is the key to dealing with them. Understanding the difference between quantitative and qualitative variables is the next step.