I have two groups of data, one is a group of people at age 5 and the other set of data is the same group of people when they are 8 years old. I want to test if group two (age 8) eat more food under a certain condition, compare to when they were 5 years old.
However, I know that in general kids eat more when they are older, hence, simply a paired t-test would give me the statistical difference, but I wouldn't know if this difference is the result of the age or condition.
I'm wondering what test I can use which would take into account this.
Best Answer
In general, the approach that would be taken to this would be to have two groups of children. One group would be under the condition, and the other group would not. You would then compare the change in consumption between the children under the condition and the control children, using, for example, a two-way mixed ANOVA to determine whether there is a change in consumption after you've controlled for the natural change that occurs over time.
If you do not have a control condition, however, then there is no statistical test which can compensate for this by controlling for the natural change. All you will be able to do is to use the paired t-test, while accepting that any effect of your condition that you observe will be confounded by the natural change that may occur due to age.