We have not discussed confidence limits on effect sizes, but Ken Kelly and Keke Lai, at Notre

Dame, created an R library named MBESS to calculate such limits. Using the data in Table

13.1, compute confidence limits on the weight difference between Before and After scores.

You can obtain that simply by looking at the result of t.test(Before, After, paired = TRUE.)

Then calculate a confidence interval on the effect size (d). To do this you need to install,

and then load, the MBESS library. Then you call for the function (ci.sm). The code is shown

below. How would you interpret this result?

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data