Eco 221 Notes Exam 3 copy

# Eco 221 Notes Exam 3 copy - Eco 221 Notes Exam 3 CONFIDENCE...

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Eco 221 Notes Exam 3 CONFIDENCE INTERVAL: for the Mean (Pg Book) 90% CI = Z.05 =(1.645) b/c [ 1-P = 0.90; P = 0.10; P/2 = 0.05] therefore ZP/2 = Z.05 why [ 1- 0.05= 0.95) find 0.95 inside table = 1.645 (or 1.65 if don’t average) 95% CI = Z.025 = (1.96) b/c [1- P = 0.95; P = 0.05; P /2 = 0.025] therefore ZP /2 = Z.025 why [1-0.025 = 0.975) find .975 inside table = 1.96 99% CI = Z.005 = (2.57 ) b/c [1-c = 0.99; c = 0.01; c/2 = 0.005] therefore ZP/2 = Z.005 why [ 1- 0.005 = 0.995) find .995 inside table= 2.57 (can use 2.58 pick one) it is not negative value. See last page for more info (Use Z #’s 1.65, 1.96, 2.57 in CI formula for mean when st dev is known, mean can be known (usually isn’t) or unknown(sample)) (St. Dev or Var must NOT be sample) Table of Z Values (Common used in Blue) Confid ence Level Confidence Coefficient, Z value 80% 90% 95% 98% 99% 99.8% 99.9% .80 .90 .95 .98 .99 .998 .999 1.28 1.645 1.96 2.33 2.57 3.08 3.27 Formula for Mean w/st. dev known: A sample of 11 circuits from a large normal population has a mean resistance of 2.20 ohms. We know from past testing that the population standard deviation is .35 ohms. Determine a 95% confidence interval for the true mean resistance of the population. Make statement: We are 95% confident that the true mean resistance is between 1.9932 and 2.4068 ohms CONFIDENCE INTERVAL FOR THE MEAN ST. DEV UNKNOWN 1 n σ Z X ± α - 1 Note If the (population) distribution X was already

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## This note was uploaded on 04/18/2008 for the course ECO 221 taught by Professor Mostaghimi during the Fall '08 term at S. Connecticut.

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Eco 221 Notes Exam 3 copy - Eco 221 Notes Exam 3 CONFIDENCE...

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