Statistics: Informed Decisions Using Data (4th Edition)

Published by Pearson
ISBN 10: 0321757270
ISBN 13: 978-0-32175-727-2

Chapter 12 - Section 12.1 - Assess Your Understanding - Applying the Concepts - Page 595: 13b

Answer

$X^2\gt X_α^2$: the null hypothesis is rejected. Thus there is significant evidence that the first digits of the checks do not obey Benford's Law.

Work Step by Step

$H_0:~the~digits~obey~Benford’s~Law$ $H_1:~the~digits~do~not~obey~Benford’s~Law$ Total frequency: $36+32+28+26+23+17+15+16+7=200$ Expected count of 1: $200\times0.301=60.2$ Expected count of 2: $200\times0.176=35.2$ Expected count of 3: $200\times0.125=25$ Expected count of 4: $200\times0.097=19.4$ Expected count of 5: $200\times0.079=15.8$ Expected count of 6: $200\times0.067=13.4$ Expected count of 7: $200\times0.058=11.6$ Expected count of 8: $200\times0.051=10.2$ Expected count of 9: $200\times0.046=9.2$ $X^2=Σ\frac{(O_i-E_i)^2}{E_1}=\frac{(36-60.2)^2}{60.2}+\frac{(32-35.2)^2}{35.2}+\frac{(28-25)^2}{25}+\frac{(26-19.4)^2}{19.4}+\frac{(23-15.8)^2}{15.8}+\frac{(17-13.4)^2}{13.4}+\frac{(15-11.6)^2}{11.6}+\frac{(16-10.2)^2}{10.2}+\frac{(7-9.2)^2}{9.2}=21.693$ $k=9$. So, $d.f.=9-1=8$ $X_α^2=X_{0.01}^2=20.090$ (According to Table VII, for d.f. = 8 and area to the right of critical value = 0.01) Since $X^2\gt X_α^2$, we reject the null hypothesis.
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