Refer to the Environmental Science & Technology (Jan. 2005) study of methyl tert-butyl ether (MTBE) contamination in New Hampshire wells, Exercise 7.66. Recall that 223 wells were classified according to well class (public or private) and detectable level of MTBE (below limit or detect). The SPSS printout below gives the number of wells in the sample with a detectable level of MTBE for both the 120 public wells and the 103 private wells. 

a. Conduct a two-tailed test of hypothesis to compare the true proportion of public wells with a detectable level of MTBE to the true proportion of private wells with a detectable level of MTBE. Use α = .10. 

b. In Exercise 7.66, you compared the two proportions with a 95% confidence interval. Explain why the inference derived from the two-tailed test, part a, will agree with the inference derived from the confidence interval.

Data from Exercise 7.66

Refer to the Environmental Science & Technology (Jan. 2005) study of methyl tert-butyl ether (MTBE) contamination in New Hampshire wells, Exercise 2.12. Data collected for a sample of 223 wells are saved in the MTBE file. Recall that each well was classified according to well class (public or private) and detectable level of MTBE (below limit or detect). The accompanying SPSS printout gives the number of wells in the sample with a detectable level of MTBE for both the 120 public wells and the 103 private wells.

Data from Exercise 2.12

In New Hampshire, about half the counties mandate the use of reformulated gasoline. This has led to an increase in the contamination of groundwater with methyl tert-butyl ether (MTBE). Environmental Science & Technology (Jan. 2005) reported on the factors related to MTBE contamination in public and private New Hampshire wells. Data were collected for a sample of 223 wells. These data are saved in the MTBE file. Three of the variables are qualitative in nature: well class (public or private), aquifer (bedrock or unconsolidated), and detectable level of MTBE (below limit or detect). (Note: A detectable level of MTBE occurs if the MTBE value exceeds .2 micrograms per liter.) The data for 10 selected wells are shown in the accompanying table. Use graphical methods to describe each of the three qualitative variables for all 223 wells.

Transcribed Image Text:

DETECT * CLASS Crosstabulation Count CLASS Private Public Total DETECT Below Limit 81 72 153 Detect 22 48 70 Total 103 120 223