What is a control variable?

please i need help!What is a control variable?
This is a basic function of all scientific experimentation. The control variable is the variable you control to see how it creates an effect, the independent variable. For example, you can control what temperature you set your thermostat and how you leave your door open or closed, the control variables. How fast your room cools down is the independent variable, because a closed room can cool in a matter of seconds while an open door can make a room stay warm for minutes.What is a control variable?
Seems that people are confusing ';control variable'; with control group, or even constants.





A control variable is a variable that you measure in your study and use in your data analysis that is not the main point of your study, but may impact the results and so it can't be ignored (i.e. can't be excluded from your study).





Say, for example, that you are interested in the relationship between gender and income, hypothesizing that males make more money than females. If you go out and ask 50 men and 50 women ';how much money do you make?'; you could compare males and females in terms of income and, lo and behold, you would probably find that the men earn more money. End of story.....right? NO!





What if it is the case that men tend to be more educated than women? Could that account for the gender difference in income? Well, you could find out if you also asked your 50 men and 50 women ';how many years did you go to school?';---then, you include years of education as a control variable in your model. Maybe, after ';controlling for'; education, the difference in income between males and females dissappears (probably not, but for the sake of argument.....). Here, you have used education as a control variable in your study of gender differences in income. If you did not control for education, you might erroneously conclude that differences in income are due to gender per se, when in reality the difference (or, perhaps, part of the difference) was due to differences in education.





So, education is not why you are doing the study, it is not your primary independent variable (or predictor variable), but it is something that you should control for, a control variable.





Now, that is how the term ';control variable'; is commonly used, but different areas of study (i.e. psychology versus education versus business, etc.) use the term somewhat differently at time. For example, rather than measuring your control variable and including it in your data analysis, you could control for it in your methodology. Using the above example, rather than measuring education and controlling for it in your data analysis, you could control for it in your methodology by making sure that your males and females were the same with respect to education--perhaps by performing your study only on people who had all just graduated from college---so they all have the exact same education. Now, you don't need to measure education because everyone has the same education, and you don't need to include it in your data analysis.





Either way though, whether you statistically or methodologically control for a variable, the point is the same---it is some variable that could mess up your study so you have to do something about it, but it is not the main point of your study (otherwise it would just be one of your independent variables/predictors).





Hope that helps
in an experimet there is the constant and the variables.





Constant stay the same varables change
something about the experiment that doesnt change.....like an amount or something that will stay constant
The control is the object in the experiment that dosent experience change.