9 
influence. The latter (realized design) is a parametric description of 
the new system after being derated in view of the predictable environment 
and circumstances. 
The next step is to combine these cost- and effectiveness-models in an 
overall model of COST-EFFECTIVENESS for the system. A commonly used con- 
cept for such a model is the ratio model, the ratio being of the output 
over the input, as used in normal engineering practices to define effici- 
ency. Here, consider analogously, cost as the input and effectiveness as 
the output. This gives (see Fig 6): 
  
M = E/C S 1.0 where M is the expected value of the cost-effec- 
tiveness figure of merit, which we seek. 
  
  
  
  
COST FACTORS EFFECTIVENESS FACTORS 
Level of use 
Performance 
R&D Availability 
Inputs Cost Model Effectiveness [Reliability | 
Model - — 
[Survivability] 
E.=3C, E =[PC,][ACa HH 
x apt 
[RCr HSCg] 
  
  
  
  
  
  
  
  
Performance 
  
m 
A I 
Location [Expected Cost| | Expected Effectiveness| 
x = 
  
COST-EFFECTIVENESS 
A uu DECISION 
M = E/C<1.0 
  
  
  
  
  
  
  
Figure 6 : System Cost-Effectiveness 
  
With this concept, a simple plot of alternatives with respect to their 
cost and effectiveness can help the management to readily identify solu- 
tions of different types (see Fig 7); eg., 
1) For a desired cost (held fixed), the alternative with maximum effe- 
ctiveness (point 1); 
2) For a desired (minimum) effectiveness, the alternative with mini- 
mum cost (point 2); or 
3) Alternative with maximum efficiency or merit (point 3); etc. etc. 
  
ue EN al A 
8-1 Max 1 
uo o3 | T Figure 7 
P rd d 
dU | > 
3g Cost-Effectiveness 
£e n | | Plot of Alternatives 
ue a -———— ———— a 
e Min 2 | 
E] O | 
| | 
  
  
Expected value of Cost