Why is a control group necessary in the experimental method?

why is a control group necessary in the experimental method?|||The control group allows you to make sure the experiment ran properly. When doing an experiment where you are changing something, you need a standard that you know how it will turn out to ensure everything worked and that the experiment wasn't bad. If you don't have a control, you can't be certain the data is valid as you don't have any evidence that the experiment worked properly. If you have a control and the results of the control are not normal, you know you can't trust your other results for the groups with the variable.|||It depends on what you are trying to do with your experiment. There are many types of experiments where, as the first answer said, you need a control group to check that there was no unknown factor or combination of factors which changed the conditions for the entire experiment. There are also very valid experiments which do not require a control group. One example of these types of experiments would be in engineering where the goal is to determine if paricular factors (or the interaction of factors) changes the distribution of the output, either moving the average higher or lower or moving the amount of variation around the average larger or smaller or both. hope this helps