EV Formulas
Submitted by pmplearner1977 on Thu, 03/21/2013 - 01:35
The formulas for EV is different between each source. For example, in Rita for
1. atypical EAC I could see AC + (BAC - EV) whereas in the below link AC + BAC - EV
2, Current variances are typical to future plus modified by performance
Rita - AC + (BAC - EV) / (CPI^c + SPI^c) whereas in the below link it is EAC = AC + (BAC – EV) / (CPIc
x SPIc
Please throw some light on this. I am confused. I dont want to choose a wrong answer just because wrong application of formula.
http://www.i-leadonline.com/elearning/advancedpm/week2/downloads/Earned%...
Forums:
bpatel
Thu, 03/21/2013 - 01:47
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Yes even i want advice from
Yes i have also came across different formulas at different places and even i want advice from experts especially one's those who have given the exam that which formulas will be useful for us in Exam so we can memorize them
sspawar
Thu, 03/21/2013 - 07:57
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You have taken it from RITA
You have taken it from RITA 6.
IN RITA 7 it has been corrected with X sign in place of + sign.
PMBOK also use X sign,
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but PMBOK add one more peculiar thing :P185
" Variations of this method weigh the CPI and SPI in different value. (e.g. 80/20 or 50/50 or any other ratio) according to project manager's judgments.."
I would like to drag attention of prominent degnatories, that how these ratios can be implimented in any case. can somebody explain it by an numeric example?
pmpnewster
Thu, 03/21/2013 - 09:11
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I am no prominent dignitary
I am no prominent dignitary hehe..., but I will say that if the CPI and SPI are to be assigned weights when both CPI and SPI appear as a PRODUCT ( i.e. CPI * SPI) in a formula, then the weights should appear in the form of exponents, i.e. CPI^0.8 or SPI^0.2 or something similar.
HOWEVER, I am not sure that the EV formulae in their present form lend themselves to such usage. I would say the formulae first need to be modified/generalized. There needs to be some normalization embedded in the formula before it can be used in that fashion.
I am sure this method is already being used... Maybe someone in the electrical utility industry can shed some light??
Regards.
sspawar
Thu, 03/21/2013 - 09:57
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CAN ANYBODY TAKE ON THIS
CAN ANYBODY TAKE ON THIS QUERY?
REFRE P 185 OF PMBOK AND PLEASE GIVE AN NUMERIC EXAMPLE HOW CPI AND SPI WILL BE IN A RATIO?
bkthakkar
Thu, 03/21/2013 - 10:58
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BAC 1000
sspawar
Sat, 03/23/2013 - 04:14
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I am talking only - how will
I am talking only - how will you divide CPI and SPI in ratio like 80/20 or 50/50.
in your example needed part is not touched.
see here
CPI=0.95
SPI = 1.03
BAC-EV = 380
Now let us know how CPI and SPI will be applied as 80/20?
bkthakkar
Sat, 03/23/2013 - 13:55
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Dear Pawar, You have to guide
Dear Pawar,
You have to guide here, if I am wrong on this interpretation
BAC-EV = 380 which means 380/1000 = 38% is impacting towards CPI and balance 62% for SPI
Hope i am correct
Regards
Bhavesh
sspawar
Sat, 03/23/2013 - 16:15
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I have no authentic
I have no authentic explanation / or literature.
by guess only
80% of affected value 380, will be divided by CPI, where 20% of affected value 380 will be divided by SPI, and both value then will be summed up.
=> (0.80*380/0.95 ) + (0.20*380/1.03)
=> (0.80 * 400) + (0.20 * 368.93)
=> 320 + 73.79
=> 393.79
-------------------------
in case of 50/50
=> (0.50*380/0.95 ) + (0.50*380/1.03)
=> 1/2(400+368.93)
=> 384.47
----------------------------------
in case of 100% impact of both:
=> 380/(0.95 *1.03)
=> 388.35
pmpnewster
Sun, 03/24/2013 - 02:09
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As I had mentioned in my
As I had mentioned in my previous post, if CPI and SPI appear as a product (i.e. CPI * SPI) then their weightages should normally appear in the form of exponents (i.e. raised to the power of) e.g. (CPI)^(weight of CPI) and (SPI)^(weight of SPI).
Also, if CPI and SPI appear as a product then they should remain as a product. We cannot switch between product in some cases and addition in other cases.
Moreover, the line from PMBOK seems to indicate that the weights should add up to 1(one).
80/20 => 0.8 + 0.2 = 1.0, or
50/50 => 0.5 + 0.5 = 1.0
So we cannot have both of 100% weight, but we can have both of equal weight (i.e. 50/50) The basic formula in PMBOK seems to have CPI and SPI weighted equally.
As I said earlier, I don't believe the present formula is general enough to support weightage. Someone, somewhere seems to have done it, since PMBOK says project managers use it in this fashion. I just hope that the project managers are not using crude approximations.
Maybe the weightage to CPI and SPI is beyond the scope of the present PMP exam, unless the formula or some guidance is provided in the question itself. Who knows, maybe the next revision of PMBOK will have a more general formula or some guidance rules.
sspawar
Sun, 03/24/2013 - 07:19
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I agree with you.Thanks for
I agree with you.Thanks for showing interest.
weightage will be incorporated in form of exponents.
second thing , PMBOK 5 -- also has same verdicts. There is no change in this respect.
In case of pure multiplication - as the original formula = BAC-EV/ SPI*CPI, this exponent theory will also not exist. Because, SPI*CPI means = SPI ^1 * CPI ^1, If it is equal weightage then what is 0.50/0.50 , if it is 100/100 then in your wor, it is not partial weightage of 100%.
I scheduled a calculation table comparing exponent weightage system with amount sharing system.
As per exponent theory
100/00
80/20
50/50
0/100
100/100
CPI^RATIO
0.95
0.960
0.975
1.000
0.950
SPI^RATIO
1
1.006
1.015
1.030
1.030
(CPI^R)*(SPI^R)
0.95
0.965
0.989
1.030
0.979
Amount of 380
400
393.584
384.152
368.932
388.350
As per amount share
100/00
80/20
50/50
0/100
100/100
Amount of 380
380/0.95
0.80*380/0.95
0.50*380/0.95
0/0.95
0.95
0/1.03
0.20*380/1.03
0.50*380/1.03
380/1.03
1.03
0.9785
Total
400
393.79
384.47
368.932
388.3495