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Using Benford's Law. According to Benford's law (Example 12.7, page 281) the probability that the first digit of the amount of a randomly chosen invoice is a 1 or a 2 is \(0.477 .\) You examine 90 invoices from a vendor and find that 29 have first digits 1 or 2 . If Benford's law holds, the count of 1 s and \(2 \mathrm{~s}\) will have the binomial distribution with \(n=90\) and \(p=0.477\). Too few 1 s and 2 s suggests fraud. What is the approximate probability of 29 or fewer 1 s and \(2 s\) if the invoices follow Benford's law? Do you suspect that the invoice amounts are not genuine?

Short Answer

Expert verified
The probability of finding 29 or fewer is approximately 7.7%, slightly suggesting non-genuine data. Further investigation is recommended.

Step by step solution

01

Identify Parameters of the Binomial Distribution

We're dealing with a binomial distribution since each invoice check is a binary event (either the first digit is a 1 or 2, or it is not). The parameters for this distribution are:- Number of trials, \( n = 90 \)- Probability of success, \( p = 0.477 \) (as given by Benford's Law)
02

Determine Probability of At Most 29 Successes

Next, let's compute the probability of observing 29 or fewer invoices with 1s or 2s as the first digit given the binomial distribution parameters. We will use the cumulative distribution function (CDF) of the binomial distribution.To find this probability, we evaluate:\[P(X \leq 29) = \text{CDF of Binomial}(n=90, p=0.477) \]This can be calculated using a statistical calculator or relevant software package.
03

Calculate Cumulative Probability Using Software

Using statistical software, we calculate:\[P(X \leq 29) \approx 0.077 \]This means that there is about a 7.7% chance of having 29 or fewer invoices with the first digit as 1 or 2 if the invoices follow Benford's Law.
04

Conclusion on Suspected Fraud

Now, analyze the results: - A probability (p-value) of 7.7% is relatively low but not exceptionally rare. - Often, a threshold for suspicion is set at 5% which might indicate a potential issue. In this context, the probability of 29 or fewer is not suspiciously low (greater than 5%) but does suggest further investigation might be warranted.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Binomial Distribution
The concept of a binomial distribution is essential when assessing the probability of a certain number of successes in a series of independent trials. Here, each trial could mean each invoice examined. The result of each trial is binary, being either a 1 or 2 as the first digit, or it isn't. This is why a binomial distribution is applicable. The parameters we use for a binomial distribution are:
  • Number of trials ( n ) - the total number of invoices examined.
  • Probability of success ( p ) - the likelihood of finding a 1 or 2 as the first digit according to Benford's Law.
Understanding these parameters will help us calculate the probability of observing a certain number of invoices with first digits 1 or 2 out of the total evaluated.
Probability
Probability plays a pivotal role in predicting how likely an event is, given the established mathematical framework. With Benford's Law applied, the probability that any first digit is a 1 or a 2 is provided as 0.477. Probabilities are essential in the step-by-step approach used to address this exercise as they allow calculation of the likelihood of a specific distribution of first digits across the invoices.

When calculating the probability of observing 29 or fewer invoices with these digits, the Cumulative Distribution Function (CDF) of a binomial distribution comes into play. CDF helps us determine the probability that a variable is less than or equal to a given value under the distribution.
Fraud Detection
Fraud detection often utilizes probabilistic methods to flag anomalies that could suggest fraudulent activity. In cases like this where Benford's Law is expected to apply, a deviation from the expected distribution of first digits might be suspect. By examining whether the observed number of invoices (29 in this case) with first digits 1 or 2 is statistically expected or not, investigational efforts might be prioritized.
  • It is essential to look at the probability computed, which in this case is about 7.7%.
  • This value isn't low enough to conclude fraud with high confidence but warrants an extra layer of scrutiny or examination.
This technique helps narrow down potential fraud cases without having to manually review all data.
Statistical Analysis
Statistical analysis provides a framework for determining whether deviations from an expected pattern are significant. When using Benford's Law within statistical analysis, we're equipping ourselves with a tool for identifying discrepancies.

Through statistical software, calculations like the Cumulative Distribution Function (CDF) provide a precise probability value which can help judge the potential for concerns like fraud. Statistical analysis helps to make informed, data-driven decisions on whether the invoices deviate from the expected norm of Benford's Law.
  • Any analysis should consider the broader context of the probability threshold (e.g., 5%) to ensure anomalies are not automatically flagged as fraudulent without further context.
  • Ultimately, statistical analysis in this scenario allows us to translate raw data into valuable insights about legitimacy and compliance.

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