MATH 324: Statistics Fall 2023 Assignment 1
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Department of Mathematics and Statistics
MATH 324: Statistics
Fall 2023
Assignment 1
Q1. Suppose that Y1 , Y2 , . . . , Yn constitute a random sample from a population with probability density function
Suggest a suitable statistic to use as an unbiased estimator for θ .
Hint: Consider Y.
Q2. The number of breakdowns per week for a type of minicomputer is a random variable Y with a Poisson distribution and mean λ. A random sample Y1 , Y2 , . . . , Yn of
observations on the weekly number of breakdowns is available.
a. Suggest an unbiased estimator for λ .
b. The weekly cost of repairing these breakdowns is C = 3Y + Y2 . Show that E(C) = 4λ + λ2 .
c. Find a function of Y1 , Y2 , . . . , Yn that is an unbiased estimator of E(C).
[Hint: Use what you know about Y and (Y)2 .]
Q3. We have seen that if Y has a binomial distribution with parameters n and p, then Y/n is an unbiased estimator of p. To estimate the variance of Y , we generally use n(Y/n)(1 - Y/n).
a. Show that the suggested estimator is a biased estimator of V (Y).
b. Modify n(Y/n)(1 - Y/n) slightly to form an unbiased estimator of V (Y).
Q4. Let Y1 , Y2 , . . . , Yn denote a random sample of size n from a population whose
density is given by
where α > 0 is a known, ixed value, but θ is unknown. Consider the estimator θˆ =max(Y1 , Y2 , . . . , Yn ).
a. Show that θˆ is a biased estimator for θ .
b. Find a multiple ofθˆ that is an unbiased estimator of θ .
c. Derive MSE(θˆ).
Q5. If Y has a binomial distribution with parameters n and p, then ˆ(p)1 = Y/n is an
unbiased estimator of p. Another estimator of p is ˆ(p)2 = (Y + 1)/(n + 2).
a. Derive the bias ofˆ(p)2 .
b. Derive MSE(ˆ(p)1 ) and MSE(ˆ(p)2 ).
c. For what values of p is MSE(ˆ(p)1 ) < MSE(ˆ(p)2 )?
Q6. Suppose that E(θ(ˆ)1 ) = E(θ(ˆ)2 ) = θ , Var(θ(ˆ)1 ) = σ 1(2), and Var(θ(ˆ)2 ) = σ2(2) ,. Consider the estimator θ(ˆ)3 = aθ(ˆ)1 + (1 - a)θ(ˆ)2 .
a. Show that θ(ˆ)3 is an unbiased estimator for θ .
b. If θ(ˆ)1 and θ(ˆ)2 are independent, how should the constant a be chosen in order to minimize the variance ofθ(ˆ)3 ?
c. How should the constant a be chosen to minimize the variance of θ(ˆ)3 if θ(ˆ)1 and θ(ˆ)2 are not independent but are such that Cov(θ(ˆ)1 , θ(ˆ)2 ) = c 0?
2023-12-14