A controlled variable remains constant and does not change throughout an experiment, while the term “uncontrolled” applies to studies where scientists can’t be certain that their test subjects are receiving the treatment in question. Evidence gathered during uncontrolled studies can thus be inconclusive. The independent variable in an experiment is directly manipulated by the scientist, and the dependent variable fluctuates in response to direct changes made in the independent variable.
Even though only the dependent variable in an experiment fluctuates, all variables must be carefully monitored. Otherwise, it is impossible to tell which variable influenced the results of the experiment. It is most helpful when the variables can be measured in terms of their mass, volume, temperature or other such calculable statistics.
For example, in an experiment to determine the freezing rate of saltwater in comparison to freshwater, the temperature would be a controlled variable, measured in Celsius or Fahrenheit. Both samples would be kept at the exact same temperature throughout the experiment. The independent variable would be the salt content in the water samples. The first sample would contain a certain amount of salt, while the second would be free of salt. The dependent variable would be the time it takes for both samples to freeze. The samples would be monitored at regular intervals to determine which sample froze more quickly.