Quality Associates Inc.

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Hypothesis Tests Case Problem 1: Quality Associates, Inc. 1. H0: µ = 12 H: µ ≠12 The hypothesis testing results are shown below: Sample 1 Sample 2 Sample 3 Sample 4 Sample Size 30 30 30 30 Mean 11.959 12.029 11.889 12.081 Standard Deviation 0.220 0.220 0.207 0.206 Level of Significance (alpha) 0.010 0.010 0.010 0.010 Critical Value (lower tail) -2.576 -2.576 -2.576 -2.576 Critical Value (upper tail) 2.576 2.576 2.576 2.576 Hypothesized value 12 12 12 12 Standard Error 0.040 0.040 0.038 0.038 Test Statistic -1.027 0.713 -2.935 2.161 p-value 0.2 -0.4 0.4-1 0-0.01 0.01-0.02 Sample 1 calculations (with same calculations for sample 2, 3, and 4): Mean: 368.76/30 = 11.959
 Standard Deviation: (11.959 - 11.55)2 + (11.959 - 11.62)2 … (11.959 - 12.15)2 = 1.408
√(1.408/30 - 1) = 0,220
 Critical Value: Because = 0.01, /2 = 0.005 = -2.576 (lower tail) and 2.576 (upper tail)
 Standard Error: 0.22/√30 = 0.04
 Test Statistic: 11.959-12/(0.22/√30) = -1.027
 p-value: DF:29 and 1.027 is between .2 and.1. These should be timed 2 because its two tailed. Therefore, P is between 0.2 and 0.4. We will reject only sample 3 of the hypothesis H0: µ = 12 because it is operating below the desired mean with a mean of 11.889 and the test statistic of sample 3 is -2.935, which is outside the critical value interval of -.2576 to 2.576. We fail to reject sample 1, 2 and 4 as they are operating within the critical value interval with respectively -1.027, 0.713, and 2.161. 2. The computation for the standard deviation for all four samples are shown in question 1. The sample standard deviations for all four samples are in the 0.20 to 0.22 range, which makes the assumption that the population standard deviation of 0.21 is good. 3. With = 0.01, z.005 = 2.576. Using the standard

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