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Law Enforcement: Officers Killed Chances: Risk and Odds in Everyday Life, by James Burke, reports that the probability a police officer will be killed in the line of duty is \(0.5 \%\) (or less). (a) In a police precinct with 175 officers, let \(r=\) number of police officers killed in the line of duty. Explain why the Poisson approximation to the binomial would be a good choice for the random variable \(r .\) What is \(n ?\) What is \(p ?\) What is \(\lambda\) to the nearest tenth? (b) What is the probability that no officer in this precinct will be killed in the line of duty? (c) What is the probability that one or more officers in this precinct will be killed in the line of duty? (d) What is the probability that two or more officers in this precinct will be killed in the line of duty?

Short Answer

Expert verified
(a) Yes, Poisson is suitable; \( n=175 \), \( p=0.005 \), \( \lambda=0.9 \). (b) \( P(X=0) \approx 0.417 \). (c) \( P(X \geq 1) \approx 0.583 \). (d) \( P(X \geq 2) \approx 0.218 \).

Step by step solution

01

Determining Parameters for Poisson Approximation

The Poisson approximation is a good choice when the probability of success (p) is very small, and the number of trials (n) is large. In this problem, \( n = 175 \) (the number of police officers) and \( p = 0.005 \) (0.5% chance of being killed in the line of duty). We calculate \( \lambda \) by using the formula \( \lambda = n \times p \), which yields \( \lambda = 175 \times 0.005 = 0.875 \). This Poisson approximation is appropriate since \( p \) is small, and \( n \) is reasonably large.
02

Calculating Probability of No Deaths

The probability of exactly 0 deaths is given by the Poisson probability formula: \( P(X=k) = \frac{\lambda^k e^{-\lambda}}{k!} \). Setting \( k = 0 \) gives us \( P(X=0) = \frac{0.875^0 \cdot e^{-0.875}}{0!} = e^{-0.875} \approx 0.4169 \).
03

Calculating Probability of One or More Deaths

The probability of one or more deaths can be found by subtracting the probability of zero deaths from 1. Thus, \( P(X \geq 1) = 1 - P(X=0) = 1 - 0.4169 = 0.5831 \).
04

Calculating Probability of Two or More Deaths

The probability of two or more deaths is calculated by subtracting the probability of zero or one death from 1. First, compute the probability of exactly one death using the Poisson formula: \( P(X=1) = \frac{0.875^1 \cdot e^{-0.875}}{1!} \approx 0.3647 \). Then, \( P(X \geq 2) = 1 - (P(X=0) + P(X=1)) = 1 - (0.4169 + 0.3647) = 0.2184 \).

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Key Concepts

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

Probability Theory
Probability theory is the mathematical framework that deals with random events and the likelihood of their occurrence. It's crucial in understanding and modeling situations that involve uncertainty.
In probability theory, each possible outcome of a situation is assigned a probability, which is a number between 0 and 1. A probability of 0 means the event will not occur, while a probability of 1 indicates certainty that an event will happen.
Understanding probability theory allows us to quantify risk and make informed decisions. This is particularly important in fields such as finance, insurance, and risk management.
Key concepts within probability theory include:
  • Sample Spaces: The set of all possible outcomes.
  • Events: A subset of the sample space.
  • Probability Functions: Assigns a probability to each event.
  • The Law of Large Numbers: Over many trials, the relative frequency of an event converges to the probability of the event.
Probability theory underpins many statistical methods, including those used for approximations such as the Poisson and Binomial distributions.
Binomial Distribution
The binomial distribution is a discrete probability distribution used to model binary (two possible outcomes) processes. Each experiment within this process is called a trial, where the outcome can either be a 'success' or 'failure'.
Mathematically, a binomial distribution process is characterized by two parameters:
  • Number of Trials (\(n\)): The total number of experiments.
  • Probability of Success (\(p\)): The likelihood of a single trial resulting in success.
The probability of getting exactly \(r\) successes in \(n\) experiments can be calculated using the formula:\[P(X=r) = \binom{n}{r} p^r (1-p)^{n-r},\] where \(\binom{n}{r}\) is the binomial coefficient.
This distribution is essential for tasks in probability theory where only two outcomes are possible, such as a flipped coin test, where the outcomes would be heads or tails. It forms the basis for approximations like the Poisson approximation, especially when the probability of success is small, and the number of trials is large.
Statistical Approximation
Statistical approximation is a powerful tool that allows statisticians to simplify complex probability problems by using simpler distributions. This is particularly useful when direct calculation using more cumbersome distributions is overly complex or impractical.
One of the key approximations in statistics is the Poisson approximation to the binomial distribution. This approximation is valid when:
  • The number of trials (\(n\)) is large.
  • The probability of success (\(p\)) is small.
  • The product of the number of trials and the probability of success (\(\lambda = np\)) is a reasonable integer.
In our police precinct scenario, using the Poisson approximation with \(\lambda = 0.875\) makes calculating probabilities more straightforward compared to using a binomial distribution every time, as it reduces computational complexity. This approximation simplifies the analysis of infrequent events over many trials.
Risk Analysis
Risk analysis involves the identification, assessment, and prioritization of risks, followed by the application of resources to minimize, control, and monitor the probability of undesirable events. It is a critical area that uses statistical and probability methods to forecast and mitigate potential risks.
In the context of our problem, risk analysis helps us understand the likelihood of police officers being harmed in the line of duty and allows decision-makers to create strategies to mitigate these risks.
By examining probabilities, such as the likelihood of one or more officers being killed, organizations can implement policies and protective measures to improve safety. Key processes in risk analysis include:
  • Identifying potential risks and understanding their causes.
  • Assessing the likelihood and impact of these risks.
  • Prioritizing risks based on their impact and likelihood.
  • Implementing strategies to minimize potential risks.
  • Continuously monitoring risks to adjust strategies accordingly.
Through effective risk analysis, organizations can make informed decisions to protect resources and personnel, reducing the chances of adverse outcomes.

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Most popular questions from this chapter

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