Project triangle

The Project Triangle

Commonly referred to in engineering is the project triangle, shown here:

You are given the options of Fast, Good and Cheap, and told to pick any two. Here Fast refers to the time required to deliver the product, Good is the quality of the final product, and Cheap refers to the total cost of designing and building the product. This triangle reflects the fact that the three properties of a project are interrelated, and it is not possible to optimise all three – one will always suffer. In other words you have three options:

• Design something quickly and to a high standard, but then it will not be cheap.
• Design something quickly and cheaply, but it will not be of high quality.
• Design something high quality and cheaply, but it will take a long time.

This constraint seems to apply to any creative human activity, such as software, movies, books etc.

There is a mathematical reason behind all this. You can work out the relationship between quality q, time t and cost c as follows:

q = art

Where r is the resource available (ie people) and a is some constant. The more time and effort we expend on the project the higher the quality.

But c = br

I.e. the cost is proportional to the amount of resource required.

For any given project the resource available is generally fixed, so by eliminating it from the equations we get:

c = bq/at

So cost is proportional to quality divided by time. Hence to lower the cost you either reduce the quality or increase the time.