Why is it advisable to use a control in an experiment?

Question

Why is it advisable to use a control in an experiment?

Answer 1

That is the only way to ensure that an outside element didn't affect your results.  Plus you need a "bench mark" for comparison.

Answer 2

A control in your experiment gives you something to compare your experimental data to. Without a control, you might think that you can compare it to how it originally was or how you thought it would be without the experimental factor, but 1) how it originally was isn't always how it would turn out without the experimental factor and 2) it serves as physical evidence, such that you can document "how it is without that factor". Also, ideas on how it would be aren't good enough for experiments where everything has to be documented.

For example, say you were testing the effect of varying amounts of pesticides on a tulip as measured by height of the tulip. Pot #1 would be your control. You would give it a tulip seed, soil, water, ___ weeks to grow, and 6 hours of light from a 60W bulb per day (these are your controlled variables) but NO pesticides. (Your experimental variable is 0 in amount for your control). Pot #2 might be your tulip that has been given 1 teaspoon of Brand A pesticide. You give it all the same controlled variables as pot #1 plus a tsp of pesticide. Pot #3 might be the same as pot #2 but has 2 teaspoons of Brand A pesticides, and so on. By having pot #1 as your control, you'll know how high the tulip can possibly grow. If pot #2's tulip is 3 inches shorter than pot #1's tulip, you'll know that that one tsp of pesticide caused the tulip to be 3 inches shorter than it could be.

I hope that helps. And if you're going to do any experiment, make sure to replicate the experiment at least 3 times (3 pot #1s, 3 pot #2s, etc) but usually more (I did 6 times when I did a plant experiment).

Answer 3

Experimenting is a method of obtaining data.  In many ways the method of controlled, repeatable experimentation is the very essence of the scientific method.

The aim of a properly conducted experiment is to create an artificial, reproducible situation in which the factor (variable) to be studied can be isolated and observed. This is not quite as easy as it sounds. Therefore, the design of an experiment becomes extremely important. The first care of the experimenter must be to ensure that he/she has in fact set up a truly reproducible situation - its importance cannot be over-stressed. If observations are not repeatable, then our observations and explanations are likewise unreliable and therefore useless.