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Owner: naweiss@sc
Created: Dec 14, 2010
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ES8 Report 06.4

You can use StatCrunch to obtain a normal probability plot. To illustrate, we discuss the StatCrunch solution to Example 6.14 of your text.

Example   Normal Probability Plots

Adjusted Gross Incomes    The Internal Revenue Service publishes data on federal individual income tax returns in Statistics of Income, Individual Income Tax Returns. A simple random sample of 12 returns from last year revealed the adjusted gross incomes, in thousands of dollars, shown in Data set 1. Construct a normal probability plot for these data, and use the plot to assess the normality of adjusted gross incomes.

Data set 1. Adjusted gross incomes (\$thousands)   [Info]

Solution   Proceed as follows.

1       Choose Graphics QQ Plot

2        Select the column AGI

3       Click Create Graph!

The output that you obtain should match that shown in Result 1. It provides the required normal probability plot of the data. Note that StatCrunch plots the sample data on the vertical axis and the normal quantiles (normal scores) on the horizontal axis.

Result 1: Normal probability plot for the sample of adjusted gross incomes   [Info]

From Result 1, we see that the normal probability plot for the sample of adjusted gross incomes is curved, not linear. Evidently, last year’s adjusted gross incomes are not normally distributed.

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