MATH 324: Statistics Midterm Fall 2023
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Department of Mathematics and Statistics
MATH 324: Statistics
Midterm Fall 2023
Q1. Let Y1 , Y2 ,... Yn denote independent and identically distributed random variables of size n from a population whose density is given by
where β > 0 is unknown. Consider the estimator β(ˆ) = Y(1) = min{Y1 , Y2 ,..., Yn}
a. Show that β(ˆ) is abiased estimator for β. (8 pts)
b. Derive the bias of the estimator β(ˆ). (4 pts)
c. Derive MSE(β(ˆ)). (6 pts)
Q2. Suppose that Y1 , Y2 , . . . , Yn denote independent and identically distributed random variables of size n from an exponential distribution with density function given by
a. Use the method of moment-generating functions to show that 2 Σ Yi/✓ is a pivotal quantity and has a χ2 distribution with 2n degrees of freedom. (8 pts)
b. Use the pivotal quantity 2 Σ Yi/✓ to derive a 95% confidence interval for ✓ (4 pts)
c. If a sample of size n = 7 yield y = 4.77, use the result from part(b) to give a 95% confidence interval for ✓. (4 pts)
Q3. a. The ages of a random sample of five university professors are 39, 54, 61, 72, and 59. Using this information, find a 99% confidence interval for the population standard deviation of the ages of all professors at the university, assuming that the ages of university professors are normally distributed. (6 pts)
b. A precision instrument is guaranteed to read accurately to within 2 units. A sample of four instrument readings on the same object yielded the measure- ments 353, 351, 351, and 355. Find a 90% confidence interval for the popu- lation variance. What assumptions are necessary? Does the guarantee seem reasonable? (10 pts)
2023-12-15