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TABLE 4. RESULTS OF HYPOTHESIS TESTS FOR EQUAL DISTRIBUTION LOCATIONS AND CONSTANT VARIANCE BETWEEN EVM AND ES METHODS Hypothesis Test Metric Stability Point (%) p-value Wilcoxon Rank Sum SPI 10 0.9448 Brown-Forsythe SPI 10 0.8261 Levene SPI 10 0.8427 Wilcoxon Rank Sum SCI 10 0.8899 Brown-Forsythe SCI 10 0.8816 Levene SCI 10 0.8900 Wilcoxon Rank Sum SPI 5 0.8967 Brown-Forsythe SPI 5 0.9549 Levene SPI 5 0.9333 Wilcoxon Rank Sum SCI 5 0.8490 Brown-Forsythe SCI 5 0.9197 Levene SCI 5 0.8817 Note. ES = Earned Schedule; EVM = Earned Value Management; SCI = Schedule Cost Index; SPI = Schedule Performance Index. Table 5 summarizes the descriptive statistics of %EAC(10) and %EAC(5) for each individual metric. This highlights how subtle the differences are between the stability results. Table 6 presents the results of the Wilcoxon Rank Sum test and Brown-Forsythe and Levene tests which, as expected, show no significant differences between the different metrics. This suggests that the rates of accuracy at estimating final cost between the metrics from both EVM and ES are comparable.
TABLE 5. SUMMARY OF MEANS, STANDARD DEVIATIONS, AND CONFIDENCE INTERVALS FOR STABILITY RESULTS OF INDIVIDUAL METRICS
Stability Point (%)
Standard Deviation
Metric
Mean
Lower Bound Upper Bound
CPI
10
72.279
17.859
65.214
79.344
SPI($)
10
72.168
21.360
63.718
80.618
SCI($)
10
70.577
19.903
62.704
78.451
SPI(t)
10
71.934
22.411
63.069
80.799
SCI(t)
10
71.016
20.289
62.990
79.042
CPI
5
84.138
14.179
78.529
89.747
SPI($)
5
83.754
14.953
77.839
89.669
SCI($)
5
83.261
15.364
77.183
89.339
SPI(t)
5
83.779
14.797
77.926
89.633
SCI(t)
5
83.477
14.606
77.699
89.255
Note. CPI = Cost Performance Index; SCI = Schedule Cost Index; SPI = Schedule Performance Index.
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Defense ARJ , Spring 2025, Vol. 32 No. 1
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