58 CHAPTER 2 Exploring Data with Tables and Graphs assessing normality—that is, determining whether the sample data are from a normally distributed population. Section 6-5 includes a procedure for constructing normal quantile plots, which are easy to generate using technology such as Statdisk, Minitab, XLSTAT, StatCrunch, or a TI-83>84 Plus calculator. Interpretation of a normal quantile plot is based on the following criteria: Criteria for Assessing Normality with a Normal Quantile Plot Normal Distribution: The population distribution is normal if the pattern of the points in the normal quantile plot is reasonably close to a straight line, and the points do not show some other systematic pattern that is not a straight-line pattern. Not a Normal Distribution: The population distribution is not normal if the normal quantile plot has either or both of these two conditions: ■ The points do not lie reasonably close to a straight-line pattern. ■ The points show some systematic pattern that is not a straight-line pattern. The following are examples of normal quantile plots. Procedures for creating such plots are described in Section 6-5. Normal Distribution: The points are reasonably close to a straight-line pattern, and there is no other systematic pattern that is not a straight-line pattern. Not a Normal Distribution: The points do not lie reasonably close to a straight line. Not a Normal Distribution: The points show a systematic pattern that is not a straight-line pattern. Histograms Access tech supplements, videos, and data sets at www.TriolaStats.com TECH CENTER Statdisk 1. Click Data in top menu. 2. Select Histogram from the dropdown menu. 3. Select the desired data column. 4. Click Plot. 5. Move the cursor over the histogram to view frequencies. 6. Select User Defined under Plot Options to use your own class width and starting point. Tip: This procedure is also an easy way to identify frequencies in a frequency distribution. StatCrunch 1. Click Graph in the top menu. 2. Select Histogram from the dropdown menu. 3. Select the desired data column. 4. To customize the histogram enter desired starting point and class width under Bins. 5. Click Compute!. Minitab 1. Click Graph in top menu. 2. Select Histogram from the dropdown menu. 3. Select Simple histogram and click OK. 4. Click on the desired data column, then click Select and click OK. 5. Change default class width and starting point as needed by right-clicking on the graph and selecting Edit Graph. Right-click on the horizontal axis and select Edit X Scale. –Select the Scale tab to enter the location of the tick marks. –Select the Binning tab to enter the class midpoints.
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