![]() The degrees of freedom are based on the sample size. For a t-test, we need the degrees of freedom to find this value. We find the value from the t-distribution based on our decision. In practice, setting your risk level (α) should be made before collecting the data. For the energy bar data, we decide that we are willing to take a 5% risk of saying that the unknown population mean is different from 20 when in fact it is not. We decide on the risk we are willing to take for declaring a difference when there is not a difference.To make our decision, we compare the test statistic to a value from the t-distribution. The figure below shows a histogram and summary statistics for the energy bars. We decide that the t-test is an appropriate method.īefore jumping into analysis, we should take a quick look at the data. ![]()
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