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As an example of a situation in which several different statis tics could reasonably be used to calculate a point estimate, consider a population of N invoices. Associated with each invoice is its 鈥渂ook value,鈥 the recorded amount of that invoice. Let T denote the total book value, a known amount. Some of these book values are erroneous. An audit will be carried out by randomly selecting n invoices and determining the audited (correct) value for each one. Suppose that the sample gives the following

\({\rm{T}}\)- sample mean book value

\(\bar X\)- sample mean advised value

\({\rm{\bar D}}\)- sample mean errors

Propose three different statistics for estimating the total audited (i.e., correct) value-one involving just N and,another involving T, N, and \({\rm{\bar D,}}\) and the last involving T and \({\rm{\bar X/\bar Y}}{\rm{.}}\)If \({\rm{N = 5000}}\)and T=1,761,300, calculate the three corresponding point estimates. (The article "Statistical Models and Analysis in Auditing," Statistical Science, 1989: 2-33 discusses properties of these estimators.)

Short Answer

Expert verified

a.The estimated value is\({\rm{1,704,000}}\).

b.The estimated value is\({\rm{1,591,300}}\).

c.The estimated value is\({\rm{1,601,438}}{\rm{.281}}\).

Step by step solution

01

Concept introduction

The standard deviation (SD) is a measure of the variability, or dispersion, between individual data values and the mean, whereas the standard error of the mean (SEM) is a measure of how far the sample mean (average) of the data is expected to differ from the genuine population mean. Always, the SEM is smaller than the SD.

02

Calculating the total audited values

The total audited values are denoted by\({\theta _T}\).

First, using simply\(N\)and\(\bar X\)the following statistic can be employed.

\({{\rm{\hat \theta }}_{{{\rm{T}}_{\rm{1}}}}}{\rm{ = N \times \bar X}}\)

Which is simply the \(N\) invoice multiplied by the average.

Second, using\({\rm{N \times \bar X}}\), and\(\bar D\), the following statistic can be employed.

\({{\rm{\hat \theta }}_{{{\rm{T}}_{\rm{2}}}}}{\rm{ = T - N \times \bar D}}\)

When the total sample mean error is deducted from the total book value, the total book value is the result.

Third, using \(T\)and \(\bar X/\bar Y\),the following statistic can be employed.

This is the quotient of the sample mean audited value and the sample mean book average multiplied by the total book value: \({{\rm{\hat \theta }}_{{{\rm{T}}_{\rm{3}}}}}{\rm{ = T \times }}\frac{{{\rm{\bar X}}}}{{{\rm{\bar Y}}}}\)

03

Estimating the point using the invoice table

Consider the given,

\(\begin{array}{l}{\rm{N = 5000 }}\\{\rm{T = 1,761,300}}\end{array}\)

The point estimations can be determined using the invoice table and the invoice table

\(\begin{array}{c}{\rm{\bar y = }}\frac{{\rm{1}}}{{\rm{5}}}{\rm{(300 + 720 + 526 + 200 + 127)}}\\{\rm{ = 374}}{\rm{.6}}\end{array}\)

The average audited value in the sample is

\(\begin{array}{c}{\rm{\bar x = }}\frac{{\rm{1}}}{{\rm{5}}}{\rm{(300 + 520 + 526 + 200 + 157)}}\\{\rm{ = 340}}{\rm{.6,}}\end{array}\)

Where the standard deviation of the sample mean error is

\(\begin{array}{c}{\rm{\bar d = }}\frac{{\rm{1}}}{{\rm{5}}}{\rm{(0 + 200 + 0 + 0 - 30)}}\\{\rm{ = 34}}\end{array}\)

As a result, the point estimations

\(\begin{array}{c}{\rm{\& }}{{{\rm{\hat \theta }}}_{{{\rm{T}}_{\rm{1}}}}}{\rm{ = N \times \bar x = 5000 \times 340}}{\rm{.6}}\\{\rm{ = 1,704,000,}}\\{\rm{n\& }}{{{\rm{\hat \theta }}}_{{{\rm{T}}_{\rm{2}}}}}{\rm{ = T - N \times \bar d = 1,761,300 - 5,000 \times 34}}{\rm{.0}}\\{\rm{ = 1,591,300,}}\\{{{\rm{\hat \theta }}}_{{{\rm{T}}_{\rm{3}}}}}{\rm{ = T \times }}\frac{{{\rm{\bar x}}}}{{{\rm{\bar y}}}}\\{\rm{ = 1,761,300 \times }}\frac{{{\rm{340}}{\rm{.6}}}}{{{\rm{374}}{\rm{.6}}}}\\{\rm{ = 1,601,438}}{\rm{.281}}\end{array}\)

Therefore, the required estimated value is\({\rm{1,601,438}}{\rm{.281}}\).

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M: 3.7 3.4 3.7 4.0 3.9 3.8 3.4 3.6 3.1 4.0 3.4 3.8 3.5
F: 3.8 2.6 3.2 3.0 4.3 3.5 3.1 3.1 3.2 3.0

  1. Compare and contrast the diameter observations for
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The National Health and Nutrition Examination Survey (NHANES) collects demographic, socioeconomic, dietary, and health related information on an annual basis. Here is a sample of \({\rm{20}}\) observations on HDL cholesterol level \({\rm{(mg/dl)}}\) obtained from the \({\rm{2009 - 2010}}\) survey (HDL is 鈥済ood鈥 cholesterol; the higher its value, the lower the risk for heart disease):

\(\begin{array}{l}{\rm{35 49 52 54 65 51 51}}\\{\rm{47 86 36 46 33 39 45}}\\{\rm{39 63 95 35 30 48}}\end{array}\)

a. Calculate a point estimate of the population mean HDL cholesterol level.

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d. An HDL level of at least \({\rm{60}}\) is considered desirable as it corresponds to a significantly lower risk of heart disease. Making no assumptions about the shape of the population distribution, estimate the proportion \({\rm{p}}\) of the population having an HDL level of at least \({\rm{60}}\).

The cdf for \({\rm{X( = measurement error)}}\) of Exercise \({\rm{3}}\) is

\({\rm{F(x) = }}\left\{ {\begin{array}{*{20}{c}}{\rm{0}}&{{\rm{x < - 2}}}\\{\frac{{\rm{1}}}{{\rm{2}}}{\rm{ + }}\frac{{\rm{3}}}{{{\rm{32}}}}\left( {{\rm{4x - }}\frac{{{{\rm{x}}^{\rm{3}}}}}{{\rm{3}}}} \right)}&{{\rm{ - 2}} \le {\rm{x < 2}}}\\{\rm{1}}&{{\rm{2}} \le {\rm{x}}}\end{array}} \right.\)

a. Compute \({\rm{P(X < 0)}}\).

b. Compute \({\rm{P( - 1 < X < 1)}}\).

c. Compute \({\rm{P(}}{\rm{.5 < X)}}\).

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e. Verify that \(\widetilde {\rm{\mu }}{\rm{ = 0}}\).

Here is a stem-and-leaf display of the escape time data introduced in Exercise 36 of this chapter.

32

55

33

49

34


35

6699

36

34469

37

3345

38

9

39

2347

40

23

41


42

4

a. Determine the value of the fourth spread.

b. Are there any outliers in the sample? Any extreme outliers?

c. Construct a boxplot and comment on its features.

d. By how much could the largest observation, currently 424, be decreased without affecting the value of the fourth spread?

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