Scientists use control groups to show how something will change under normal circumstances. For example, if they are measuring the height of plants, the control will be giving it adequate sunlight and water. The other groups might receive water with specific nutrients. That will show how much the plants that recieved nutrients differed from the plant that grew in normal circumstances. In other words, the control group is used to compare results with the other groups....
Controlled experiment means you keep every other variable constant, except for one ( the one being tested). A variable means something that varies, or keep changing. Controlled experiment removes all the possibilities of external influences on the subject. Everything else must remain constant in a controlled experiment, that's how you will able to study it in its true context.
Because if you run a trial after altering two variables, you will make the data difficult to interpret.
For example, if my lamp doesn't turn on and I attempt to find out what is wrong with it (experiment), I can immediately change the light bulb, try a different power outlet, manuever the cord, and flick wall switches (trials). When I turn on the lamp and it works, I will not be able to interpret the data (cause of lamp failure).
However, if I take the same experiment and control it, test ONE variable at a time, I can rule out causes of failure as I try them and the lamp remains non-functional. With a controlled experiment, I can immediately recognize the problem as the last variable I changed before the lamp turned on.
Similarly, a control is needed for a valid experiment because each variable may have a different effect on the outcome. If we limit each trial by changing only one variable (control), we can observe how EACH variable affects the outcome and by what quantity.
Experiments usually require a control so that we can compare our results with the control experiments. This greatly helps us to understand, analyze and predict results concerning the specific experiment or practical.
Suppose after several days, three fertilized plants grow between 2 and 3 cm. If one of the plants is unfertilized and it grows 1.5 cm, you might infer that the growth of the fertilized plants was due to the fertilizers.
Control is the portion that you are not performing experiments on. It is just there to serve as the blank state that experiments compare to. For instance, in a drug trial, the control group are giving placebos and data from the experimental group that actually took the drug will be compared to it to see effects.
In an experimental design, the variable over which the researcher has control, and which is different for the treatment and control groups, is called the _____.
