This is the second in a series of posts on commonly confused terms for PMP exam.
PMBOK® Guide 5th Edition defines:
Assumption – A factor in the planning process that is considered to be true, real, or certain, without proof or demonstration.
Constraint – A limiting factor that affects the execution of a project, program, portfolio, or process.
Assumptions and constraints are first listed in the Project Charter and then analysed and expanded throughout the project. They form an important component of the project scope statement; their validity should be tested throughout the project.
As stated in the definition above, constraints define the boundaries imposed by the client/sponsor or by government regulations due to the nature of the work. Constraints can be business constraints imposed by the organisation, typically related to time, cost, schedule, resources, quality, or risk tolerances; or, technical constraints imposed by the design and architecture of the system, like hardware constraints in software development, strength of the materials for construction of a bridge, etc. Constraints are key inputs to the development of WBS, time and cost management processes, and risk management process.
Assumptions are factors that we believe to be true without any definite proof or analysis. Assumption analysis is a key input to the risk management process. We make assumptions every day in every aspect of our lives, assuming the traffic on the way to work will be same as last week, markets will recover the highs after a long bear run, milk will always be stocked and available at a 24 hr grocery store, people working for 7.5 hours will actually work effectively and efficiently for 7.5 hours, etc.
Another way to look at assumptions are factors that must occur for the project to succeed, with the probability of an assumption holding its weight between 0 (assumption turns to be completely false) and 1 (exactly as assumed). Using assumptions help to model a project for cost and time estimates. However, if the probability of an assumption turns out to be 0, the estimates and the whole project may be in jeopardy. That is the reason why assumptions are a critical input to risk management and setting up of contingency and management reserves.
Let’s look at an example:
You are a PM for a condo restoration project following a flood due to water main rupture. This is a major undertaking involving several stakeholders with competing requirements. Constrains imposed by the condo board and condo management company can include, all work on the condos should be accomplished by the year end and the budget for the project is limited to the insurance claim plus a percentage of the reserve fund as stipulated in the condo by laws. Another constraint could be that an inspection should be completed before the hallway walls can be insulated and dry walled. Some assumptions in this project can be – the next condo will become available as soon as the work on the last one is finished, no delays in the shipment and availability of materials, all the owners who renovated their units followed the condo by laws, etc.
Many times you may realize that constraints imposed on a project are also the result of assumptions made by sponsor/client/regulators.
An interesting word history on assumption from dictionary.reference.com (of course not required for PMP!):
The word assumption is a great example of how a word can take on new dimensions of meaning over time, while staying true to some aspect of its original sense. Assumption has been in the language since the 13th century, and was initially confined to a specific ecclesiastical meaning in the Catholic Church. The Latin word on which it is based literally means “the action of being taken up or received,” and in English assumption referred to the taking up into heaven of the Virgin Mary. That meaning still exists today, and in all the meanings it has assumed since then, one can see the common thread running through them is the sense of taking.
One early sense meant “arrogance,” as in this 1814 quote from Sir Walter Scott: “his usual air of haughty assumption.” Arrogance is a taking upon oneself a conviction of self-importance. Later senses arose having to do with the taking on of power or other responsibilities, as in “the assumption of command.”
Probably the most common meaning of assumption in use today is for indicating a supposition, an estimate, a conjecture—that is, something taken for granted. And as any school kid knows, presuming to assume can be dangerous, leading us to make, as the saying goes, “an ASS of U and ME!”