Monday, June 9, 2008

Project Cost Performance Measurement Techniques

One of the most important aspects of project cost control is cost performance measurement. You can use a number of performance measurement techniques to measure cost performance, including cost variance, earned value management (EVM), and the cost performance index. Details about these three cost performance measurement techniques are provided below.

1. Cost variance
Cost variance (CV) is the most basic performance measure. Simply stated, cost variance is the difference between the earned value and actual costs. A positive variance indicates that the project is running under budget, while a negative variance means that costs are overrunning. For the purpose of tracking over- or underrun percentages, you may want to use tables, Gantt charts, or bar charts.

Cost variance is typically expressed as a ratio or percent. You can calculate CV by comparing the actual cost of the work (AC) to the earned value (EV). Follow the steps below to calculate cost variance.
  • Calculate the difference between the earned value of the project and the actual costs.
  • Divide this amount by the earned value.
  • Multiply this figure by 100 to obtain a percentage.
  • Keep the negative sign for cost overruns.
The project manager's goal in calculating variances is to provide the basis for earned value management. You must understand the problems behind variances and take action that will correct any problems.

2. Earned value management
Earned value management is perhaps the most useful activity in cost control because it combines costs and the schedule into one indicator. It tells you how much the project is physically accomplishing in terms of both cost and time, giving management a more accurate and timely report on project progress.

The concept of earned value management multiplies the project budget (planned value, or PV) and percent-complete figures to arrive at a budgeted dollar value of the work that has actually been completed so far. The main difficulty in using earned value data to measure cost performance is in determining work completion. How does one accurately measure how much of a task is complete, while avoiding subjectivity in measuring performance as much as possible?

There are five methods you can use to assess work completion. They are described below, from the most conservative and least accurate to the most accurate.
  • The zero/100 rule. Many companies do not assess percent complete incrementally. This removes any subjectivity. A task is assessed as either not done (zero percent complete) or finished (100 percent complete). This method works well for activities with a short duration—less than a month, for example.
  • The 20/80 rule. This method is almost as conservative as the zero/100 rule. When it is started, a task is considered to be 20 percent complete, and 20 percent of the PV is charged against its account. When the task is complete, the remaining 80 percent of the budget is applied to the task.
  • The 50/50 rule. This is probably the most popular method. You assume that once a task has begun, 50 percent of its budget is used. When a task is complete, it has used the other half. For a project with a large number of tasks, this method provides a fairly accurate way to calculate earned value.
  • The milestone method. This is used for long work packages that are broken down into distinct milestones. A budget is assigned to each milestone instead of to the task as a whole. Value is earned when each milestone is completed.
  • The percent complete. This method is usually used for long-duration work packages (for example, ones that last three months or more). Your project may not have identifiable milestones, but you are still able to estimate the percentage of the task that has been completed.
3. The cost performance index
You can use the earned value figure to establish another important performance indicator. Calculate the ratio of earned value to the actual costs to find out how efficiently your team is accomplishing the work. This ratio is called the cost performance index (CPI). The formula for calculating CPI is as follows:

CPI = EV ÷ AC.

When the CPI is measured periodically, you can plot CPI figures in a line graph to see the trend over the life of the project. This is called a trend analysis.

You will usually see the cost performance index reported along with its "companion" indicator—the schedule performance index (SPI). The SPI is the ratio of earned value (EV) to the planned costs (PV).

Project managers use the CPI and SPI to rate the cost and schedule performance of their projects. A poor rating provides a warning signal, allowing for corrective action to be taken before it's too late. These indexes fall into three categories:
  • If equal to 1.0, performance is exactly as planned.
  • If greater than 1.0, performance is better than planned.
  • If less than 1.0, performance is poor.
Evidence shows that without corrective action, most projects will continue to perform at their cumulative CPI rate. Once the project is about one-third complete, you will have difficulty recovering from a CPI of less than 1.0 without aggressively managing the remaining tasks.

Remember, it's important to measure the cost performance of your projects. By using the three techniques described above, you can control project costs and ensure the project comes in on-budget.

1 comment:

jr1 said...

Equivalent units is a useful EV method. There are not just 5 and the %complete method is the least effective as it's the easiest to "game" the system. Also, I may be wrong, but I didn't see any mention of the importance of the Performance Baseline and the EV methods being part of it and thus subject to change control.