Refer to the Environmental Science & Technology (Jan. 2005) investigation of MTBE contamination in 70 New Hampshire groundwater wells, Exercise 14.33 (p. 14-22). Recall that the level of MTBE contamination was compared for private and public wells and for bedrock and unconsolidated aquifers. The environmental researchers also investigated how the combination of well class and aquifer affected the MTBE levels of the wells. Although there are four possible combinations of well class and aquifer, there were data available for only three: Private/bedrock, Public/bedrock, and Public/unconsolidated. The distribution of MTBE levels for these three groups of wells was compared using the Kruskal-Wallis nonparametric test for independent

samples.The SAS printout for this analysis is shown on p. 14-40. Interpret the results for the researchers. Explain why your choice of a for this analysis is critical.

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The NPARIWAT Procedure Wi Icoxon_Scores (Rank Sums) for Variable MTBE Classified by Variable wellaqa Expected Under HO Std Dev Under HO Sum of Scores Mean Score we llaq Private/Bedro 22 654.50 139.50 1691.00 781.00 79.027002 51.06964G 83.856064 29.750000 Public/Uncon Public/Bedroc 248.50 19.928571 1455.50 41.243902 41 Average scores vere used for ties. Kruskal-Wallis Test Chi-Square DF Pr > Chi-Square 9.1244 0.0104