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advice please on guestimating confidence levels

4 replies [Last post]
Gary Whitehead
User offline. Last seen 1 year 39 weeks ago. Offline
I’m working on a project with a critical sectional completion date of 31/3/14
On the critical path is release of a key area by another project
This other project is approx 18 month’s work, but it’s start is being delayed by client due to financial approval
Plugging in the delayed start of this other project gives us approx 12 weeks float on our sectional completion. This represents approx 5% of the total time from now to 31/3/14
I don’t have access to the other project programme, and I can’t find any details on why the finanical approval of it is being delayed

So that’s the situation. I want to povide a confidence level that my project will hit it’s completion date, but without the details behind financial approval activities and the other’s project’s programme, I don’t know how to go about running a Monte Carlo analysis or anything.

Any suggestions or rules of thumb I could apply here? I haven’t done much schedule risk analysis before, so I don’t want to have to trust my gut feel.

Thanks in advance,



Rafael Davila
User offline. Last seen 5 hours 16 min ago. Offline
Joined: 1 Mar 2004
Posts: 5000

At your initial posting you expressed you desire not to include details of the schedule as you do not have access to the other project programme, but now I see you have access to more than a single milestone.

If these milestones are FS dependant in tandem maybe the compromise could be to use them as your summary activities, each with a different distribution. This will provide you with the opportunity to update the Monte Carlo run after each of these events happen. As with any schedule you will only get a prediction, a prediction that will vary with time, a prediction that will depend on your client estimates for probable durations.

The resulting distribution will provide you with a rough estimate of how much of terminal float to use, your selection will be based on a probabilistic distribution, not a deterministic number, your final choice will be based on how risk adverse you are.

This is as far as I can go, good luck.

Best regards,
Gary Whitehead
User offline. Last seen 1 year 39 weeks ago. Offline
Thanks gents for your replies

The problem I have is how best to represent the key external delivery miestone for monte carlo purposes.

The CP to the delivery milestone is:
-Client funding approval process
-Contract Award for EPC Project A
-EPC project A approx 80% complete
-Area released for my project

I was worried that representing this entire path using a single activity would be too simplistic to get sensible results from the monte carlo? Especially as I know so little about them.
My gut feel is that these predecessors have a fairly high risk of overrun, and we would want at least 10% terminal float on our project to mitigate this risk to say a 95% confidence level.
NB: This is not to mitigate risk of LDs, but the risk to the client of late delivery of a project required by it’s regulator.


Rafael Davila
User offline. Last seen 5 hours 16 min ago. Offline
Joined: 1 Mar 2004
Posts: 5000

If you are using Primavera software at a click of a button you can transfer your job into Primavera Pertmaster. Then you must add your duration distributions for each activity but you might choose a few that automatically determine the distribution form the single deterministic duration. Now you are ready to rumble.

After you run the Monte Carlo Simulation you will get your job deterministic duration as well as the probabilistic distribution. You will find the probabilistic distribution shifted to the right of the deterministic duration. This is due to the fact that at times non critical activities are delayed and become the critical path. That is another reason why many schedules are optimistic.

Believe me the theory is not difficult to understand, because there is no mathematical way to estimate total job distribution for duration you have no other option than use Monte Carlo, this will run your job hundreds or thousands of times with different combinations of individual activities duration based on their individual duration distributions and from this you will get the distribution. Help from within Pertmaster should be enough.

The software should provide you with parameters that will show the probability of non critical activities becoming critical. One of these should be the delivery activity form your external job. I suggest using a single long duration activity for this purpose with a wide spread duration distribution, also a distribution shifted to the right of the initial deterministic duration.

Get your hands dirty with Pertmaster, in no time you will be up and running.


Brad Lord
User offline. Last seen 6 years 39 weeks ago. Offline
Joined: 27 May 2003
Posts: 256
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hi gary

I did the monte carlo thing along time ago, based on the most likely, optimistic and pessemistic durations, these were gleamed from the project team. and fed into p3, anyway will you be using Primavera and Monte Carlo Risk Analysis Software?