Lab6 - Geog 306, Spring 2008 Lab 6 Problems April 4/April...

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Geog 306, Spring 2008 Lab 6 Problems April 4/April 11/April 17 Solve these problems twice. First, calculate the following using R (or by hand), but do not use any of the “.test” commands. Then, solve the following problems using the appropriate test – t.test, wilcox.test, aov.test, oneway.test, kruskal.test, or any other of the “.test” commands that are correct for the individual problem. Use both parametric and nonparametric approaches. 1. Consumer Reports tested the stopping distances (in feet) of 10 Firestone Winterfire tires and 12 Michelin XM+S Alpin tires when traveling on ice at 15 mph with the following results. Can you conclude that there is a difference the mean stopping distances of the two kinds of tires? Winterfire: x 1 = 51 ft; s 1 = 8 ft; n 1 = 10 Alpin: x 2 = 55 ft; s 2 = 3 ft; n 2 = 12 2. Determine whether the numbers of invertebrate species above and below a sewage outflow are different in a variety of rivers according to this data. River Above outflow Below outflow A 8 6 B 9 9 C 12 11 D 8 4 E 15 10 F 7 8 G 14 10 H 5 5 I 7 6 J 11 10 Test to use: t test Non Parametric: Wilcoxon Signed Rank test Commands: di = river$Above - river$Below di hist(di) dbar=mean(di) dbar n = length(river$Above) sd = sqrt( (sum ((di-dbar)^2)) / (n -1) ) sigma = sd/sqrt(n) t = dbar/sigma t
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Lab6 - Geog 306, Spring 2008 Lab 6 Problems April 4/April...

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