Distribution Comparisons of EAC Cost Growth
Rayleigh, Weibull, beta, and triangular distributions by WBS element. Lower values of AIC suggest a better distributional fit to the WBS cost growths, while higher AIC values suggest a poorer fit. As evident in some cases (e.g., between the lognormal and Weibull curves for the Cost WBS cost growths), the AICs are similar suggesting a possible tie for which distribution is the better fit. Despite this possible equivalency, we do rank each distributional fit by ascending AIC score by WBS element; a value of 1 indicates the lowest AIC fitting, while 5 is the highest. Table 5 reflects those rankings in addition to the mean ranking of each distribution, amalgamated across all WBS elements.
TABLE 4. AIC DISTRIBUTION FITTING BY WBS ELEMENT
WBS Element
Lognormal AIC
Rayleigh AIC
Weibull AIC
Beta AIC
Triangular AIC
Cost Data
99.87
123.93
99.16
147.78
125.88
81.37
88.81
73.96
65.25
72.63
Fee
80.61
137.51
83.66
116.83
119.36
PME
126.38
166.10
127.01
185.63
166.39
SE
66.29
83.68
32.19
85.57
76.16
SEPM
159.02
234.11
158.82
227.57
242.01
ST&E
139.08
147.95
145.37
162.15
154.83
Training 51.98 Note. AIC = Akaike Information Criterion; PME = Prime Mission Equipment; SE = Support Equipment; SEPM = Systems Engineering and Program Management; ST&E = System Test and Evaluation; WBS = Work Breakdown Structure. 38.40 49.29 40.53 57.41
TABLE 5. AIC RANKINGS BY WBS ELEMENT
WBS Element
“Best” Fit
Lognormal AIC
Rayleigh AIC
Weibull AIC
Beta AIC
Triangular AIC
Cost Data
Weibull
2
3
1
5
4
Beta
4
5
3
1
2
Fee
Lognormal
1
5
2
3
4
PME
Lognormal
1
3
2
5
4
SE
Weibull
2
4
1
5
3
SEPM
Weibull
2
4
1
3
5
ST&E
Lognormal
1
3
2
5
4
Training
Lognormal
1
3
2
5
4
Mean/Mode Rank
Lognormal
1.75
3.75
1.75
4
3.75
Note. AIC = Akaike Information Criterion; PME = Prime Mission Equipment; SE = Support Equipment; SEPM = Systems Engineering and Program Management; ST&E = System Test and Evaluation; WBS = Work Breakdown Structure.
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Defense ARJ , Spring 2025, Vol. 32 No. 1
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