Saturday, August 21, 2010

What is an independent variable? a dependent variable? controlled variable?

The independent variable is the variable that changes or can be changed





The dependent variable changes according to the independent variable





eg. If they were testing to see the amount of ice cream sold on a hot day was greater then the amount sold on a cold day:





Idependent Variable = Temperature of the day (hot or cold)


Dependent Variable = Amount of ice cream sold





Have fun!! =DWhat is an independent variable? a dependent variable? controlled variable?
These terms refer to experimental research (i.e. research that can identify cause and effect, not just correlation). In any experiment, you measure something while manipulating something else to see if there is a casual link. Genrally, the thing that you measure is dependent on the thing that you manipulate and this tells you which are the dependent and the independent variables.





For example, if you were to do an experiment in which you test short term memory among people who have or have not taken a caffeine tablet then you are experimenting to see if short term memory abilities are affected by (i.e. dependent on) taking caffeine or not. You allocate people into two groups (randomly) and give one group a caffeine table and the other group a (sugar pill). You then get them to do a short-term memory test. Memory test result is the dependent variable and whether or not they got caffeine is the independent variable.





Controlled variables are other things that you think might affect the outcome which you need to control, even though they are not part of the experiment. For example, you might think smoking might affect the result so you may want to control smoking status either by choosing all non-smokers, by getting all participants to agree they will not smoke during or for half-an-hour before the test, or by recording smoking status and whether they smoker during the test and factoring this into your statistical analysis. Either way, smoking status and smoking behaviour become controlled variables.





Summary: In any experiment, you expect the result (dependent variable) to be dependent on the thing you manipulate (independent variable) and there may be other factors that you need to take control of so they don't mess things up (controlled variables).

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