Chapter 11 Inferences about Populations Variances Chapter 11 Inferences About Population Variances Case Problem: Air Force Training Program Some descriptive statistics about the current and proposed methods are as follows: Variable N Mean SE Mean StDev Current 61 75.066 0.505 3.945 Proposed 61 75.426 0.321 2.506 Minimum Q1 Median Q3 Maximum 65.000 72.000 76.000 78.000 84.000 69.000 74.000 76.000 77.000 82.000 The sample mean of 75.066 and 75.426 hours show that both methods have approximately the same mean completion time. The standard deviations of 3.945 hours for the current method and 2.506 hours for the proposed method show the proposed method has less variation. A test of the difference between population means with H0 : μ 1-2 = 0 has a t value of -.60 and a corresponding p-value of .548. Thus, at α = .05, the null hypothesis cannot be rejected. The sample evidence does not indicate the methods differ in terms of mean completion times. The 95% confidence interval estimate of the difference between two population means is -1.55 to .83 hours.
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