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For this module, you will need to obtain more data.  As you did in Module 7, visit the United States Environmental Protection Agency’s download daily data page at http://www.epa.gov/airdata/ad_data_daily.html new window.  Collect data with the same parameters as you did before but for one thing; this time collect data for 2011.   When you download this data, save it to a new Excel file.  Look in your data set for the AQS_Parameter_Code column.  If you have two different measuring methods, please remove the data for one of them.  Having done this, copy this data into a new tab in the worksheet you were using for Module 7.  Give this new tab a descriptive name. 

For this new data, use Excel’s COUNTIF function to find the number of days with a PM2.5 AQI value over 50.  Use this to find the proportion of days for which the air quality was not good in your sample.  You will need to know the number of successes, the sample size, and the proportion of successes for to continue.

Create a new tab in your worksheet and label it “Mod 8”.  Perform a four-step hypothesis test (hypothesize, prepare, compute to compare, and interpret) to test whether the proportion of days which do not have “Good” air quality has changed.  Insert any work done using StatCrunch into your Mod 8 tab.  Tech Tips for using StatCrunch can be found at the end of Chapter 8. Include clear verbal explanation for each of the steps.