6-5 Assessing Normality 297 Step 4: We now pair the original sorted Dallas commute times with their corresponding z scores. We get these 1x, y2 coordinates, which are plotted in the accompanying Statdisk display: 110, -1.282, 116, -0.522, 120, 02, 125, 0.522, 130, 1.282 Statdisk INTERPRETATION We examine the normal quantile plot in the Statdisk display. The points do appear to lie reasonably close to the straight line, so we conclude that the sample of five commute times does appear to be from a normally distributed population. YOUR TURN. Do Exercise 5 “Ages of Presidents.” Ryan-Joiner Test The Ryan-Joiner test is one of several formal tests of normality, each having its own advantages and disadvantages. Statdisk has a feature of Normality Assessment that displays a histogram, normal quantile plot, the number of potential outliers, and results from the Ryan-Joiner test.
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