Oil spill impact on seabirds. Refer to the Journal of Agricultural, Biological, and Environmental Statistics

(Sept. 2000) study of the impact of a tanker oil spill on the seabird population in Alaska, presented in Exercise 2.205

(p. 138). Recall that for each of 96 shoreline locations

(called transects), the number of seabirds found, the length

(in kilometers) of the transect, and whether the transect was in an oiled area were recorded. (The data are saved in the EVOS file.) Observed seabird density is defined as the observed count divided by the length of the transect.

A comparison of the mean densities of oiled and unoiled transects is displayed in the MINITAB printout on the next page. Use this information to make an inference about the difference in the population mean seabird densities of oiled and unoiled transects.

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MINITAB output for Exercise 9.127 Two-Sample T-Test and CI: Density, Oil Two-sample T for Density Oil N Mean StDev SE Mean no 36 3.27 6.70 yes 60 3.50 5.97 1.1 0.77 Difference mu (no) mu (yes) Estimate for difference: -0.221165 95% CI for difference: (-2.927767, 2.485436) T-Test of difference = 0 (vs not =) T-Value = -0.16 P-Value 0.871 DF = 67