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In high risk projects both individual task costs and durations as well as task dependencies are hard to evaluate. Risk effects can be modeled by Monte Carlo -method.
Method relies on repeated random sampling to obtain numerical results - e.g. for project cost and duration. The underlying concept is to use randomness to solve problems that might be deterministic in principle. Results are accurate enough when number of sampling rounds is sufficiently high.
Project is calculated several times during the planning phase. For every round each project task gets random cost and duration values, which are sampled from task specific distributions.
The attached picture shows how random costs from different rounds are distributed between minimum (in the example 100€) and maximum (in the example 1200€) values, when task cost follows so called beta-PERT distribution. Random costs fall typically close to the most probable cost in the distribution. Same logic applies to task duration.
The result after large number of repetitions will be the probability distributions for total project cost and duration. These distributions are usually shown with histograms and cumulative probabilty distribution curves. Histogram shows how many times total project cost or duration falls into certain interval and cumulative distribution curve shows the probability of staying below a certain total project cost or duration.
Attached picture shows how to view results for total project cost.
Correlation coefficients can be used to show how much project's total cost or duration depends on the cost or duration of each task. Attached picture shows a Pearson correlation coefficient for cost. It can have values between -1 (maximum reverse correlation) and +1 (maximum positive correlation).
Attached scatter chart shows the cost and duration of each iteration round. Number of hits shown in the chart depends on the number of simulation rounds. Scatter charts are useful for estimating the probability of staying simultaneously below certain cost and duration limits.
Example were created with the MonteCarloProject, which is a project management application with Monte Carlo simulation. It has free basic features and can be extended with simulation plan.