Listed below are amounts of strontium-90 (in millibecquerels, or mBq, per gram o
ID: 3387071 • Letter: L
Question
Listed below are amounts of strontium-90 (in millibecquerels, or mBq, per gram of calcium) in a simple random sample of baby teeth obtained from Pennsylvania residents and New York residents born after 1979 (based on data from “An Unexpected Rise in Strontium-90 in U.S. Deciduous Teeth in the 1990s,”) by Mangano, et al., Science of the Total Environment). Use a 0.05 significance level to test the claim that the median amount of strontium-90 from Pennsylvania residents is the same as the median from New York residents. Use the Wilcoxon rank-sum test.
Pennsylvania:
155
142
149
130
151
163
151
142
156
133
138
161
New York:
133
140
142
131
134
129
128
140
140
140
137
143
Pennsylvania:
155
142
149
130
151
163
151
142
156
133
138
161
New York:
133
140
142
131
134
129
128
140
140
140
137
143
Explanation / Answer
Correct Answer: Option (D)
high rank = 194.5 = W
mean = n1(n1+n2+1) /2 = 150
Variance = n1n2(n1+n2+1) / 12 =300
Z= (194.5 - 150) / sqrt(300) = 2.57
Critical z: ±1.96
P-value = P(z<-2.57) + P(z>2.57) = 0.0051+0.0051 = 0.0102
Since p-value is less than 0.05, reject the null hypothesis that the populations have the same median.
Ranks Pennsylvania New york Pennsylvania New york 1 155 133 22 5.5 2 142 140 15 11.5 3 149 142 18 15 4 130 131 3 4 5 151 134 19.5 7 6 163 129 24 2 7 151 128 19.5 1 8 142 140 15 11.5 9 153 140 21 11.5 10 133 140 5.5 11.5 11 138 137 9 8 12 161 143 23 17 Total: 194.5 105.5Related Questions
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