If subjects have been matched on some variable such as IQ then a correlated groups t-test should be used to analyze the data.

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Matching subjects on a variable such as IQ is done to control for that variable and to make the groups as similar as possible. The correlated groups t-test is used when the two groups being compared are related to each other, such as in a pre-test/post-test design, or when subjects are matched on a variable.

If Subjects Have Been Matched on Some Variable Such as IQ