In a similar way to when controlling project scope, variance analysis is a technique used to determine how close the project performance is to the plan.
However, several additional techniques are used to measure schedule performance.
Here are the technique differences between controlling the schedule verses developing the schedule:
Schedule variance analysis compares the baseline with the actual results. You can compare several elements to determine the progress. The following is a list of common elements you can compare:
In addition, your analysis should include determining the amount of float you have used compared against how far along you are in the project.
For example, if you have 30 days of float for the project, you are halfway through, and you’ve used 21 days of float, that might be a cause for concern. You are 50% done but I have used 70% of the float.
Variance analysis should also address the root cause of the variance and whether corrective or preventative actions are desired or even possible. Here are some of the common causes of schedule variances:
Staffing variances. If you were planning to have specific resources available but they are not available, you might have a variance.
Change in priorities. When you planned the project, it was considered a high priority projects. However, things have changed. When your project is no longer high priority, your resources might be available for less time and you had planned.
Inaccurate estimating. If your duration estimates were too aggressive, you should expect a negative schedule variance.
Rate of work. Some people working really fast, and others work really slowly. The rate of work can affect how quickly you get work done.
Scope creep. Of course, if you add scope without analyzing the impact of budget and schedule, you’re most likely be behind schedule.
Often, you will present the data from the variance analysis at a performance review. Some performance reviews are very structured affairs can include the sponsor, the customer, and key vendors.
These reviews can take several hours. Other performance reviews are less formal, consisting of the project manager and the sponsor reviewing the project status.
During the performance reviews, you might present various options for correcting any negative variance is. It is common to present a earned value data at these your views as well. You would expect to present schedule variance, and schedule performance index measurements as part of your variance analysis and performance review.
Throughout the project you may revisit your resource allocation among activities to try and optimize your resources. For example, you might move some resources to activities on the critical path if you are concerned that those activities will not finish on time.
Or would you might find that work is taking longer than expected, and some resources are working 60 hour weeks. In that case, you might reduce the amount of work that they are doing.
Of course, this could have negative impacts, so you have to analyse your options and select the best one.
As the project progresses, your uncertainty in some areas will diminish, but it might increase in other areas based on the work performance. You can use what if scenario analysis much the same way you do in planning by thinking through different scenarios that could affect the project and seeing what happens to the schedule based on the scenarios.
You can use this technique along with resource leveling to see the effect of shifting resources, adding resources, or reducing the amount of time that you are using specific resources.
You can also use what if scenario analysis when analyzing the impact of risk events to see the impact on schedule if a specific risk occurs.
As you go to the project, you will probably need to find ways to compress some parts of the schedule because of the parts took longer than expected. The two types of schedule compression are crashing and fast tracking.