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Owner: websterwest
Created: Jul 20, 2007
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Views: 2400
 
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Acid rain report
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The EPA states that any area where the pH of rain is less than 5.6 on average has an acid rain problem. The pH values collected over 90 rain falls at Shenandoah National Park are given in the attached data set. Does Shenandoah National Park have an acid rain problem? Let's do a one samplet-test to find out.

First let's check the normality assumption with a histogram. Result 1 shows the dialog for creating a histogram of the pH levels.

Result 1: Snapshot of Histogram Dialog   [Info]
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Result 2 shows the resulting histogram. It looks to be roughly normal and very symmetric.

Result 2: Histogram   [Info]
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Now on to the t-test. Results 3 and 4 show the options selected for doing the test.

Result 3: Snapshot of One sample T statistics Dialog   [Info]
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Result 4: Snapshot of One sample T statistics Dialog   [Info]
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The resulting output is shown in Result 5. The p-value is very very small in this case (off the charts you might say), so we conclude that the mean pH content of rain in Shenandoah National Park is indeed below 5.6. Somebody call the EPA! :)

Result 5: One sample T statistics   [Info]
Hypothesis test results:
μ : mean of Variable
H0 : μ = 5.6
HA : μ < 5.6
Variable Sample Mean Std. Err. DF T-Stat P-value
pH_level 4.577889 0.030483205 89 -33.530304 <0.0001

Data set 1. Acid rain data   [Info]
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<A href="http://www.statcrunch.com/5.0/viewreport.php?reportid=1801">Acid rain report</A>

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