Using IRA, we can gain many valuable insights into a project and its probabilistic behaviours. These insights include, but are not limited to:
• How likely is it that the deterministic schedule and estimate will be achieved?
• What are appropriate levels of cost and time contingency in order to be x% confident of achieving project objectives within budgeted allowances?
• Which risks / uncertainties are the biggest determinants of project cost and schedule outcomes?
• What is the likely time and/or cost consequence of failing to adequately treat a known risk?
• Which execution option will likely result in the optimum balance between performance on cost and schedule objectives?
, we discussed in detail the common sources of schedule uncertainty, including quantity uncertainty, productivity uncertainty, staffing uncertainty, schedule risk events, and weather uncertainty. However, most of these are not uniquely schedule related, but usually drivers of cost also:
• Additional materials / equipment quantities require more time to install, but will also cause additional purchase and installation costs.
• Lower productivity levels result not only in schedule delays, but increased labour costs associated with prolongation also.
• Increased staffing numbers may result in a faster schedule, but at the price of increased unit per time costs.
• Schedule risk events have the potential to delay project completion, with the potential to impose significant project prolongation costs. Even risk events that occur off the critical path can still affect the cost of at least a portion of the project budget.
• Under many contracts, downtime associated with inclement weather will cause additional costs to the project. Even though no work may be getting done at site, someone usually still has to pay the workers!
• Labour rate uncertainty: This refers to the rate per unit time at which members of the labour force will be paid. There are usually two main constituents here – 1) uncertainty regarding negotiated labour rates in an enterprise bargaining agreement, and 2) uncertainty regarding the seniority of personnel with which the project will be staffed.
• Material / Equipment Price Uncertainty: Unless material and equipment orders have already been placed, there is usually uncertainty over how much they will cost to procure and deliver to site. This is usually driven by market factors such as raw material costs and market demand for the commodity in question. However, project factors such as geographical remoteness can also contribute to delivery cost uncertainties. For some equipment, even after order placement, there is often still residual cost uncertainty regarding the requirement for time of vendor representatives at site during installation / commissioning.
• Cost Risk Events: Some risk events will ultimately have significant cost impact, but little to no discernable schedule impact. For example, there may be a risk that labour force market conditions will be ‘hotter’ than expected, requiring that the project pay higher rates than expected in order to attract a sufficient quantity of quality personnel to the project. In IRA however, where a risk has both cost and schedule impacts, it is very important that prolongation costs be omitted as impacts of the risk. These costs are ultimately calculated through the risk’s schedule uncertainty acting on the time dependent costs in the model.
• Economic Factors: There are of course a multitude of economic factors that may affect the final capital costs of the project. However, perhaps one of the most commonly encountered ones is Exchange Rate Uncertainty. No project exists in a bubble, and unless exchange rates have been hedged, fluctuations in international market conditions will continue to present an exchange rate risk to any project involving exchanges in multiple currencies.