5.) An actuary discovers that policyholders are three times as likely to file 2 claims as to file 4 claims. If the number of claims filed follows a Poisson distribution, what is the standard deviation of the number of claims filed?
Q. 5.) An actuary discovers that policyholders are three times as likely to file 2 claims as to file 4 claims. If the number of claims filed follows a Poisson distribution, what is the standard deviation of the number of claims filed?
Denote probabilities and parameters: Let's denote the probability of filing 2 claims as P(2) and the probability of filing 4 claims as P(4). According to the given information, P(2)=3×P(4). In a Poisson distribution, the probabilities of different numbers of events are determined by the parameter λ (lambda), which is also the mean of the distribution. The standard deviation of a Poisson distribution is the square root of λ.
Use Poisson PMF: To find the relationship between P(2) and P(4) in terms of λ, we use the Poisson probability mass function (PMF): P(k)=k!e−λ⋅λk, where k is the number of events (claims in this case), e is the base of the natural logarithm, and k! is the factorial of k.
Set up and simplify equation: Using the Poisson PMF for P(2) and P(4), we have:P(2)=2!e(−λ)⋅λ2P(4)=4!e(−λ)⋅λ4Given that P(2)=3⋅P(4), we can set up the equation:2!e(−λ)⋅λ2=3⋅4!e(−λ)⋅λ4
Solve quadratic equation: Simplify the equation by canceling out the common terms and solving for λ:2λ2=3×24λ42λ2=8λ4Multiplying both sides by 8 to get rid of the denominator:4×λ2=λ4
Find lambda: We now have a quadratic equation in terms of λ2. Let's denote x=λ2 and solve for x: 4x=x2x2−4x=0x(x−4)=0This gives us two solutions for x: x=0 or x=4. Since λ2 cannot be 0 (as it would imply no claims are ever filed, which is not reasonable in this context), we take λ2=4.
Calculate standard deviation: Now that we have λ2=4, we can find λ by taking the square root:λ=4λ=2 Since the standard deviation of a Poisson distribution is the square root of λ, and we have found λ to be 2, the standard deviation is:Standard deviation = λStandard deviation = 2
More problems from Find probabilities using the binomial distribution