I had a spare week last year
and looked at both as well as options that use MS Project. PRA has known design limitations and some bugs that restrict
what one might expect it to be able to do but it has the design intent of being a rich modelling environment. A good
modeller who understands what they are trying to do and takes account of its limitations can do a lot with it. Not
everything one would like but quite a lot.
If I set one at a low level task and, leaving it locked, change the slider at the summary level, I take it that
the summary level factor has no effect on the detailed level task. Is that correct?
Unlike the admittedly rudimentary but nevertheless useful risk factors in PRA, it seems that I cannot
apply two or more factors to one activity. Is that correct? For instance, I might want to represent the effect of
quantity uncertainty on the duration of earthworks and separately apply a productivity uncertainty associated with the
workforce and perhaps a further factor associated with the management of the earthmoving fleet and truck reliability
.
There seems to be a strict hierarchical arrangement so that I cannot apply a single factor to a subset
of the activities under one summary item. It has to be applied to all or they each have to have their own factor.
s that correct?
3- existence allows for representation of something equivalent to a limited form of
branching, e.g. rework or no rework, but is there any true branching capability that would allow us to have two paths
from a node only one of which, with its effect on costs and overall duration, will be taken into account in a particula
r iteration.
4- the same feature, is it possible to have a whole block of activities that either occur or not, say not just rework
but rework followed by regression testing and review activities? Another example might be to construct a shallow road
tunnel using road headers to bore the passage, represented by a set of activities, or cut a way through from above as a
channel and cover the passage to make it a tunnel, which again will require a set of activities to represent it.<
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5 - risk events’ likelihoods are associated with a band of probabilities, which probability is used to model the
occurrence of the event? Is it the mid point of the range, the threshold (low point) for the range or something else.<
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6. Are risks always applied pro rata to a group of activities? Is there a way to apply a risk in the sa
me way to all activities in a group, as with a flood causing a part of a site to become isolated so that all work in t
at area stops for a couple of weeks.
7. If among my project activities I have risk events that have a 1 day impact, some that have a 5 day im
pact, some 10, some 15, some 20, an odd one that has a 30 day effect and something even worse, it seems I wouldn’t be a
ble to represent them all in the risk register because it is confined to five discrete impact levels. Is this correct? <
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8. How is correlation applied. Is it applied to all the distributions at once so that all distributions i
n a model are linked to one another?
9. I take it there is no way to correlate selected groups of activities independently of one another. <
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10. The cost risk modelling isn’t clear to me.
I presume that the cost estimate has to be imported against the same WBS as the schedule. Is this correct?
Is it possible to designate some costs as being duration dependent and some as fixed or are they all proportional to
duration?
Can a cost be partially duration dependent? This is common with contractors’ on-site facilities, for instan
ce, where some costs, such as on-site vehicles, rise as the job extends but others, such as mobilisation and demobilisat
ion, are unaffected.
11. Is there any means of applying uncertainty to calendars?