Research scientists manipulate variables in order to test their hypotheses and learn more about how the world works. Unlike in algebra, where the word "variable" refers to an unknown quantity that the mathematician is trying to identify, in research science variables are any factors or conditions that are changeable during the course of an experiment such as temperature, time or composition. Scientists attempt to change only one variable at a time so that the reasons for the results of an experiment are clear.
In research science, variables refer to factors or conditions that can change during the course of an experiment. For example, in an experiment to see how different conditions affect the temperature at which water boils, the size of the burner and pot used, amount of water, temperature at which the water is heated and any items added to the water are all variables. Scientists attempt to change only one of these variables at a time so that there is no confusion about what caused a change.
In any science experiment, there are three types of variables: independent, dependent and controlled variables.
The independent variable is the variable that the scientist manipulates. For example, if scientists are studying how putting salt in cold water affects how long it takes to boil water, the presence of salt is the independent variable.
The dependent variable is a variable that changes as the result of changing the independent variable. If water boils faster when salt is added to it, then the time water takes to boil is the dependent variable.
Controlled variables are variables that the scientist does not want to change during the course of the experiment such as the amount of water used, size of the burners and the temperature of the heating element.
When designing experiments, scientists must figure out three things: what question they hope to answer, what types of results they expect to see and what else might affect the results. The answers to these questions help them determine the independent, dependent and controlled variables in the experiment. It is especially important to make sure that controlled variables are accounted for. If the experiment design does not adequately address these variables, the results of the experiment may not be valid.
When the results of an experiment could be caused by controlled variables, these variables are known as confounding factors. It is impossible to determine whether the results of such an experiment occurred because of the scientist's manipulation of the independent variable or because of failure to control other variables.
It is best to identify controlled variables before conducting an experiment so that they can be addressed when designing a study. After planning a study, scientists should ask themselves what might cause results if their hypothesis is wrong. This helps them find and plan for controlled variables.
After a study is complete, other scientists in different areas of the country or world read about it and try to replicate the experiment. If scientists in different places get different results when doing the experiment exactly as the original scientist did, this suggests the presence of confounding factors such as quality of equipment, air quality or quality of materials used.