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(In some of the exercises that follow, we must make assumptions such as the exis

ID: 3183086 • Letter: #

Question

(In some of the exercises that follow, we must make assumptions such as the existence of normal distributions with equal variances.) Say X and Y are independent random variables with distributions that are N(mu X, sigma 2X) and N(mu Y, sigma 2Y). We wish to test H0: sigma 2X = sigma 2Y against H1: sigma 2X > sigma 2Y. (a) Argue that, if H0 is true, the ratio of the two variances of the samples of sizes n and m, S2X/S2Y, has an F(n-1,m-1) distribution. (b) If n = m = 31, x = 8.153, s_x^2 = 1.410, y = 5.917 = 0.4399, s2x/s2y = 3.2053, and alpha = 0.01, show that H0 is rejected and H1 is accepted since 3.2053 > 2.39. (c) Where did the 2.39 come from?

Explanation / Answer

2.39 is the value of F dsitribution on 0.01 level of singificance and 30 degrees of freedom for both numerator and denominator