In an investigation of environmental causes of disease, data were collected on the annual mortality rate (deaths per 100,000) for males in 61 large towns in England and Wales. In addition, the water hardness was recorded as the calcium concentration (parts per million, ppm) in the drinking water. The data set also notes for each town whether it was south or north of Derby. Is there a significant difference in mortality rates in the two regions? Here are the summary statistics.

a) Test appropriate hypotheses and state your conclusion.
b) The boxplots of the two distributions show a possible outlier among the data north of Derby. What effect might that have had on your test?

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Summary of: For categories in: mortality Derby Group North South Count 34 27 Median 1631 1369 StdDev 138.470 151.114 Mean 1631.59 1388.85 2000 1800 2 1600 1400 1200 North South Derby