In the study of software project scheduling, the Putnam–Norden–Rayleigh curve, also known as the PNR curve, is an equation specifying the relationship...
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SOFTWARE PROJECT MANAGEMENT
BY VARSHA KUMARI
, also known as the , is an equation specifying the relationship between applied effort and delivery time for a software project. A PNR curve can be used to determine the least cost time for delivery up to the limit , the absolute minimal amount of time required to complete the project
The following equation shows the relationship of project effort as a function of project delivery time.
Where =Effort in person months =The nominal delivery time for the schedule =Actual delivery time desired
We can attempt to force a flat staffing profile, but it will result in considerable waste: In the early stages, there will be people standing around with nothing to do, because the requirements and architecture development process is more gated by time than by labor. In the mid stages, work may be delayed by not having enough people available to perform all of the defined tasks. In the late stages, over-staffing will not bring the project to completion any sooner, because the collection of feedback and shaking out of final problems is (again) more gated by time than available labor.
Lawrence Putnam (of RADC) applied Norden and Rayleigh's work to the effort to quantitatively predict the work associated with software projects. After studying numerous projects, he concluded that the effort required to deliver a project varied inversely as the fourth power of the time allotted to its completion.
This curve breaks down into four zones: An impossible zone The project cannot be accomplished in less time than this, no matter how many people are applied to the problem. An "Haste makes waste" zone Adding people does accelerate delivery, but not in proportion to the added effort. Each additional person added to the project lowers our productivity (they have to be trained, more time goes into communication and coordination, more misunderstandings). This is a very inefficient way to operate.
A linear range This is the range of efficient staffing, and within this range it is possible to trade man-power for time, or vice versa. An under-staffed/over-staffed zone This curve does not yield completion time as a function of staffing, but merely shows the relationship between staffing level and completion times. What we can clearly see on the right of the curve is that productivity is dropping. Reason: ◦
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If the project is critically under-staffed, productivity will suffer because there aren't enough people to deal with the problems. if the project is greatly over-staffed communications overhead will reduce efficiency and misunderstandings will create problems and result in wasted work.
