Analyzing Stability of Estimates at Completion
60% complete and EAC SCI ($) to achieve stability within 10% deviation at approximately 20% complete. Utilizing ES metrics provided stability results similar to EVM metrics. Ultimately, the graphical analysis of cost and schedule performance stability suggests no significant difference between the different metrics in estimating cost at completion for long duration development efforts. The statistical comparisons aid in reinforcing these preliminary conclusions. Comparison Analysis Table 3 summarizes the descriptive statistics of %EAC(10) and %EAC(5) for EVM and ES. Table 4 presents the results of the Wilcoxon Rank Sum test and Brown-Forsythe and Levene tests. The comparison shows no statistically significant difference between the distributions and variances of %EAC(10) and %EAC(5) for the EVM and ES methods. This suggests the two methods have comparable accuracies in predicting final schedule for long duration development efforts.
TABLE 3. SUMMARY OF MEANS, STANDARD DEVIATIONS, AND CONFIDENCE INTERVALS FOR STABILITY RESULTS OF EVM AND ES METHODS
Stability Point (%)
Standard Deviation
Lower Bound
Upper Bound
Method Metric
Mean
EVM SPI($)
10
72.168
21.360 63.718
80.618
EVM SPI($)
5
83.754
14.953
77.839
89.669
EVM SCI($)
10
70.577
19.903
62.704 78.451
EVM SCI($)
5
83.261
15.364
77.183
89.339
ES
SPI(t)
10
71.934 22.411
63.069 80.799
ES
SPI(t)
5
83.779
14.797
77.926
89.633
ES
SCI(t)
10
71.016
20.289
62.990 79.042
ES 89.255 Note. ES = Earned Schedule; EVM = Earned Value Management; SCI = Schedule Cost Index; SPI = Schedule Performance Index. SCI(t) 5 83.477 14.606 77.699
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Defense ARJ , Spring 2025, Vol. 32 No. 1
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