The S-Curve in Project management is a form of mathematical theory, which aims to represent the utilization of resources over the proposed time of your project. The curvature illustrates the side by side comparisons of the actual expenditure components and time vs. the proposed time and costs allocations of specific resources.
An s-curve is a graphical tool that displays cumulative data ( e.g. project’s costs, quantities, hours and progress) against time. The term S-Curve denotes the tendency of the cumulative curve to form a shallow ‘S’ shape; flatter at the start, steeper in the middle, and flattening off again towards the end.
Although the s-curve derives from the S-like shape of the curve, don’t be surprised if your s-curve isn’t in the shape of an “S”. There are several shapes for S-curve which depend on the nature of the project.
Why is it “S”?
Well, the ‘S’ shape is nothing forced or developed, it’s only the shape that the graph makes when the project’s standard growth is very slow during the early stages of the project.
In the early stages, the project is starting to unravel, and the team members are just doing industry research or are just starting to engage in the first phase of project execution.
As more and more progress is made, growth suddenly begins to accelerate. If you want this rapid growth in the graph, it’ll be the middle part of the ‘S’. The point of maximum growth is called the point of inflection. These are the most important parts of the curve because this is the place where growth is stagnating.
At this stage in the process, the team members generally work quite heavily on the project tasks, and as they step up this process, more and more tasks surface, and so do their costs.
After passing the point of inflection, the growth plateau forms the upper part of the s-curve. This part is referred to as the upper asymptote. Essentially, this is the mature phase of the project.
This maturity is due to the fact that most of the projects have been completed at this point and are in the process of winding down. Generally, when the process reaches this point, only tasks such as finishing touches and final approvals are unfinished.
Types of S-curves in Project Management
There are many several types of S-curves such as man-hours vs. time and cost vs. time. The cost vs. time S-curves is useful for developing the project’s overall “cash flow”.
Another common type of S-curves is the ones generated using units/quantities vs. time. These types of s-curves are useful for comparison.
In the Construction Project Management fields, there are many S-Curves needed:
- Baseline S-Curve
- Percentage S-curves
- Baseline Ranges (Banana Curves)
- Man-hours Vs Time
- Recovery Plan Vs Actual
- Cash Flow –Plan & Actual & Forecast
- Quantity Comparisons
- Progress and Performance Evaluation
- Manpower Histogram
You may find a front-loaded s-curve, where the curve starts up steeply and then flatten out.
As explained here, front-loaded curves have a quick start. More money and resources will be consumed early in the project. This may happen for repetitive projects that need little preparation time and planning. Other examples of front-loaded curves are for projects that have been accelerated from the beginning, or projects that need an urgent repair of damage early on. Deposits and Mobilization costs will also lean toward a front-loading s-curve.
Back-loaded S-Curves are the curves that start with a lower slope and increasingly steep towards the end of the project, most resources assumed to be consumed late in the project.
A backloaded s-curve could indicate large design and planning or in the beginning and reduced construction time.
- You should verify the basis of the project plan and ensure both the schedule and the available resources are realistic.
- With the understanding of s-curves and their various shapes, now the question is “what kind of information is plotted in an s-curve?”
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