18.27 Whelks on the Pacific coast. In a study of the presence of whelks along the Pacific coast, investigators put down

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18 27 Whelks On The Pacific Coast In A Study Of The Presence Of Whelks Along The Pacific Coast Investigators Put Down 1 (90.35 KiB) Viewed 71 times

18.27 Whelks on the Pacific coast. In a study of the presence of whelks along the Pacific coast, investigators put down a frame that covers 0.25 square meter and counted the whelks on the sea bottom inside the frame. They did this at 7 locations in California and 6 locations in Oregon. The report says that whelk densities “were twice as high in Oregon as in California (mean SEM, 26.9 +1.56 versus 11.9 2.68 whelks per 0.25 m², Oregon versus California, respectively; Student's t test, P < 0.001)."13 (a) SEM stands for the standard error of the mean, s/ Vn. Fill in the values in this summary table: , s Group Location n X s 1 2 Oregon ? California ? ? ? (b) What degrees of freedom would you use in the conservative two-sample t pro- cedures to compare Oregon and California? (c) What is the two-sample t test statistic for comparing the mean densities of whelks in Oregon and California? (d) Test the null hypothesis of no difference between the two population means against the two-sided alternative. Use your statistic from part (c) with degrees of freedom from part (b). Does your conclusion agree with the published re- port?