In: Statistics and Probability
Recall that Benford's Law claims that numbers chosen from very
large data files tend to have "1" as the first nonzero digit
disproportionately often. In fact, research has shown that if you
randomly draw a number from a very large data file, the probability
of getting a number with "1" as the leading digit is about 0.301.
Now suppose you are an auditor for a very large corporation. The
revenue report involves millions of numbers in a large computer
file. Let us say you took a random sample of n = 215
numerical entries from the file and r = 49 of the entries
had a first nonzero digit of 1. Let p represent the
population proportion of all numbers in the corporate file that
have a first nonzero digit of 1.
(i) Test the claim that p is less than 0.301. Use
α = 0.05.(a) What is the level of significance?
State the null and alternate hypotheses.
H0: p = 0.301; H1: p ≠ 0.301H0: p < 0.301; H1: p = 0.301 H0: p = 0.301; H1: p < 0.301H0: p = 0.301; H1: p > 0.301
(b) What sampling distribution will you use?
The standard normal, since np > 5 and nq > 5.The Student's t, since np > 5 and nq > 5. The standard normal, since np < 5 and nq < 5.The Student's t, since np < 5 and nq < 5.
What is the value of the sample test statistic? (Round your answer
to two decimal places.)
(c) Find the P-value of the test statistic. (Round your
answer to four decimal places.)
Sketch the sampling distribution and show the area corresponding to
the P-value.
(d) Based on your answers in parts (a) to (c), will you reject or
fail to reject the null hypothesis? Are the data statistically
significant at level α?
At the α = 0.05 level, we reject the null hypothesis and conclude the data are statistically significant.At the α = 0.05 level, we reject the null hypothesis and conclude the data are not statistically significant. At the α = 0.05 level, we fail to reject the null hypothesis and conclude the data are statistically significant.At the α = 0.05 level, we fail to reject the null hypothesis and conclude the data are not statistically significant.
(e) Interpret your conclusion in the context of the
application.
There is sufficient evidence at the 0.05 level to conclude that the true proportion of numbers with a leading 1 in the revenue file is less than 0.301.There is insufficient evidence at the 0.05 level to conclude that the true proportion of numbers with a leading 1 in the revenue file is less than 0.301.
(ii) If p is in fact less than 0.301, would it make you
suspect that there are not enough numbers in the data file with
leading 1's? Could this indicate that the books have been "cooked"
by "pumping up" or inflating the numbers? Comment from the
viewpoint of a stockholder. Comment from the perspective of the
Federal Bureau of Investigation as it looks for money laundering in
the form of false profits.
Yes. The revenue data file does not seem to include more numbers with higher first nonzero digits than Benford's law predicts.No. The revenue data file seems to include more numbers with higher first nonzero digits than Benford's law predicts. Yes. The revenue data file seems to include more numbers with higher first nonzero digits than Benford's law predicts.No. The revenue data file does not seem to include more numbers with higher first nonzero digits than Benford's law predicts.
(iii) Comment on the following statement: If we reject the null
hypothesis at level of significance α, we have not proved
Ho to be false. We can say that the probability
is α that we made a mistake in rejecting
Ho. Based on the outcome of the test, would you
recommend further investigation before accusing the company of
fraud?
We have not proved H0 to be false. Because our data lead us to accept the null hypothesis, more investigation is not merited.We have not proved H0 to be false. Because our data lead us to reject the null hypothesis, more investigation is merited. We have proved H0 to be false. Because our data lead us to reject the null hypothesis, more investigation is not merited.We have not proved H0 to be false. Because our data lead us to reject the null hypothesis, more investigation is not merited.
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2.
[–/8 Points]DETAILSBBUNDERSTAT12 8.3.009.
MY NOTES
Is the national crime rate really going down? Some sociologists
say yes! They say that the reason for the decline in crime rates in
the 1980s and 1990s is demographics. It seems that the population
is aging, and older people commit fewer crimes. According to the
FBI and the Justice Department, 70% of all arrests are of males
aged 15 to 34 years†. Suppose you are a sociologist in Rock
Springs, Wyoming, and a random sample of police files showed that
of 35 arrests last month, 26 were of males aged 15 to 34 years. Use
a 10% level of significance to test the claim that the population
proportion of such arrests in Rock Springs is different from
70%.
(a) What is the level of significance?
State the null and alternate hypotheses.
H0: p ≠ 0.7; H1: p = 0.7H0: p = 0 .7; H1: p < 0.7 H0: p = 0.7; H1: p > 0.7H0: p < 0 .7; H1: p = 0.7H0: p = 0.7; H1: p ≠ 0.7
(b) What sampling distribution will you use?
The standard normal, since np > 5 and nq > 5.The standard normal, since np < 5 and nq < 5. The Student's t, since np < 5 and nq < 5.The Student's t, since np > 5 and nq > 5.
What is the value of the sample test statistic? (Round your answer
to two decimal places.)
(c) Find the P-value of the test statistic. (Round your
answer to four decimal places.)
Sketch the sampling distribution and show the area corresponding to
the P-value.
(d) Based on your answers in parts (a) to (c), will you reject or
fail to reject the null hypothesis? Are the data statistically
significant at level α?
At the α = 0.10 level, we reject the null hypothesis and conclude the data are statistically significant.At the α = 0.10 level, we reject the null hypothesis and conclude the data are not statistically significant. At the α = 0.10 level, we fail to reject the null hypothesis and conclude the data are statistically significant.At the α = 0.10 level, we fail to reject the null hypothesis and conclude the data are not statistically significant.
(e) Interpret your conclusion in the context of the
application.
There is sufficient evidence at the 0.10 level to conclude that the true proportion of arrests of males aged 15 to 34 in Rock Springs differs from 70%.There is insufficient evidence at the 0.10 level to conclude that the true proportion of arrests of males aged 15 to 34 in Rock Springs differs from 70%.
3.
[–/8 Points]DETAILSBBUNDERSTAT12 8.3.010.
MY NOTES
Women athletes at the a certain university have a long-term
graduation rate of 67%. Over the past several years, a random
sample of 36 women athletes at the school showed that 21 eventually
graduated. Does this indicate that the population proportion of
women athletes who graduate from the university is now less than
67%? Use a 10% level of significance.(a) What is the level of
significance?
State the null and alternate hypotheses.
H0: p < 0.67; H1: p = 0.67H0: p = 0.67; H1: p > 0.67 H0: p = 0.67; H1: p ≠ 0.67H0: p = 0.67; H1: p < 0.67
(b) What sampling distribution will you use?
The standard normal, since np < 5 and nq < 5.The Student's t, since np > 5 and nq > 5. The Student's t, since np < 5 and nq < 5.The standard normal, since np > 5 and nq > 5.
What is the value of the sample test statistic? (Round your answer
to two decimal places.)
(c) Find the P-value of the test statistic. (Round your
answer to four decimal places.)
Sketch the sampling distribution and show the area corresponding to
the P-value.
(d) Based on your answers in parts (a) to (c), will you reject or
fail to reject the null hypothesis? Are the data statistically
significant at level α?
At the α = 0.10 level, we reject the null hypothesis and conclude the data are statistically significant.At the α = 0.10 level, we reject the null hypothesis and conclude the data are not statistically significant. At the α = 0.10 level, we fail to reject the null hypothesis and conclude the data are statistically significant.At the α = 0.10 level, we fail to reject the null hypothesis and conclude the data are not statistically significant.
(e) Interpret your conclusion in the context of the
application.
There is sufficient evidence at the 0.10 level to conclude that the true proportion of women athletes who graduate is less than 0.67.There is insufficient evidence at the 0.10 level to conclude that the true proportion of women athletes who graduate is less than 0.67.
1)
Ho : p = 0.301
H1 : p < 0.301
(Left tail test)
The standard normal, since np > 5 and nq > 5.
Level of Significance, α =
0.05
Number of Items of Interest, x =
49
Sample Size, n = 215
Sample Proportion , p̂ = x/n =
0.2279
Standard Error , SE = √( p(1-p)/n ) =
0.0313
Z Test Statistic = ( p̂-p)/SE = (
0.2279 - 0.301 ) /
0.0313 = -2.34
p-Value = 0.0097 [excel
function =NORMSDIST(z)]
Decision: p-value<α , reject null hypothesis
At the α = 0.05 level, we reject the null
hypothesis and conclude the data are statistically significant
There is sufficient evidence at the 0.05 level to conclude that the
true proportion of numbers with a leading 1 in the revenue file is
less than 0.301.
We have proved H0 to be false. Because our data lead us to reject the null hypothesis, more investigation is not merited.
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