ch 25 - Chapter 25 Solutions 25.1(a Diagram below(b The...

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Chapter 25 Solutions 25.1. (a) Diagram below. (b) The null hypothesis is “all groups have the same mean rest period,” and the alternative is “at least one group has a different mean rest period.” The P -value shows signiFcant evidence against H 0 , and the graph leads us to conclude that caffeine has the effect of reducing the length of the rest period. Note: Students might be tempted to think that the alternative hypothesis is “mean rest period decreases with increasing caffeine dosage” or something similar, but ANOVA alternatives are nondirectional. Random assignment - - - Group 1 36 flies ± Treatment 1 Control J J J J^ © © ©* Group 2 36 flies ± Treatment 2 1mg / ml caffeine H H Hj H H Hj Group 3 36 flies ± Treatment 3 2.5 mg / ml caffeine © © ©* J J J J^ Group 4 36 flies ± Treatment 4 5mg / ml caffeine - - - Observe duration of rest period 25.2. (a) The null hypothesis is “all age groups have the same (population) mean road-rage measurement,” and the alternative is “at least one group has a different mean.” (b) The F test is quite signiFcant, giving strong evidence that the means are different. The sample means suggest that the degree of road rage decreases with age. (We assume that higher numbers indicate more road rage.) 25.3. (a) The stemplots (right) appear to suggest that logging reduces the number of trees per plot and that recovery is slow (the 1-year- after and 8-years-after stemplots are similar). (b) The means lead one to the same conclusion as in (a): the Frst mean is much larger than the other two. (c) In testing H 0 : µ 1 = µ 2 = µ 3 versus H a : not all means are the same, we Fnd that F = 11 . 43 with df = 2 and 30, which has P = 0 . 000205, so we conclude that these differences are signiFcant: The number of trees per plot really is lower in logged areas. Never logged 0 0 1 1 699 2 0124 2 7789 3 3 1 year ago 0 2 0 9 1 2244 1 57789 2 0 2 3 8 years ago 0 4 0 1 22 1 5889 2 22 2 3 276
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Solutions 277 25.4. (a) The stemplots (right) show no extreme outliers or skewness. (b) The means suggest that a dog reduces heart rate, but being with a friend appears to raise it. (c) F = 14 . 08 and P = 0 . 000 (meaning P < 0 . 0005), which means that we reject H 0 : µ P = µ F = µ C in favor of H a :a t least one mean is different. Based on the conFdence intervals, it appears that the mean heart rate is lowest when a pet is present (although this interval overlaps the control interval) and is highest when a friend is present (although again, this interval overlaps the control interval).
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This note was uploaded on 12/30/2009 for the course PSYC PSYC 60 taught by Professor ? during the Fall '09 term at UCSD.

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ch 25 - Chapter 25 Solutions 25.1(a Diagram below(b The...

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