Median real estate property taxes paid for housing units with mortgages in 2013: $590 (1.2%). Median real estate property taxes paid for housing units with no mortgage in 2013: $637 (1.5%). Nearest city with pop. 50,000+: Bismarck, ND (78.6 miles, pop. 55,532). Nearest city with pop. 200,000+: Minneapolis, MN (305.7 miles, pop. 382,618).
The third type of variable is a controlled variable. This variable is constant in an experiment. Experiments are repeated a number of times to interpret how a change in the independent variable affects each trial result.
An experiment usually has three kinds of variables: independent, dependent, and controlled. The independent variable is the one that is changed by the scientist. To ensure a fair test, a good experiment has only one independent variable. As the scientist changes the independent variable, he or she observes what happens.