Deterministic and probabilistic activity duration
Deterministic activity duration shall be calculated as follows:
Duration, TE = q* p / n
where
q = amount of work to be executed in an activity.
It may be in suitable unit, for example, cubic metre of concrete casting, kilometre of road laying, etc;
p = resource productivity standard (see 6.1.5);
and
n = number of identified resource groups that may be deployed on the activity at any time.
For example, for excavating a large area, more number of excavators can be deployed, but not so for excavation in a small area.
Contingency planning for activity durations shall include modifying the above calculated activity durations, based on:
a) Activity constraints of time, location, etc;
b) Risks foreseen for the activities; and
c) Study of the project environment and other subjective issues.
Care shall be taken to include appropriate buffer for contingencies, if required.
Probabilistic activity duration shall be calculated as follows:
Duration, TE =( a + 4 m + b)/6
where
a = optimistic duration of the activity,
m = most likely activity duration, and
b = pessimistic duration of the activity.
For assuming values of a, m and b following conditions shall apply:
a) a, m and b are positive numbers.
b) a <= m<= b.
The probabilistic activity duration may be calculated using a triangular distribution. Other form of statistical
distribution such as beta distribution may also be used to model construction activity duration.