One of the more common metrics used today for schedule quality is “Missed Tasks”. The definition of a missed task is one that either has missed, or is forecasted to miss its baseline finish date. So basically it tracks if you are executing the project to plan or not. Having no missed tasks is obviously a good thing; it is good to meet your commitments. However, there is a scenario when no missed tasks can be a bad sign.
This scenario happens when you have missed tasks on the actual side of the status date but no forecasted missed dates going forward. You could argue that you have figured out what was causing you to miss dates in the past and have corrected everything going forward…but how realistic is that? How often do we see in project management poor performance stop on a dime and not happen as of a date certain? A more likely explanation is that you are not updating the schedule going forward. You can expect at least some level of performance impact on future activities if you have consistently experienced slips in the past.
To see this, you need to look at the metric at a level other than the total project. You have to slice the project into at least two sections, past and future, and measure the metric within each of those phases independently. If all the missed tasks show up in the past phase of the project, you may have an issue.
It is even better to break the project down into more than two reasonably sized phases based on your projects overall duration. Then you will be able to see trends in the growth or decline of missed activities. The phases can be monthly if you have a 12 month project, or quarterly if you have up to a couple of years or whatever makes sense. By looking at the data this way, you can see trends for the missed tasks (or any other metric) while looking at a single instant of the project. If you are reviewing a project, this might be the only insight you have.
If you have a scenario where your project magically gets better as of the status date, or just recovers remarkably fast, you can start to look for other indicators of what is going on to diagnose the problem. For example, is the rapid recovery of missed tasks mirrored by an increase in the use of leads (negative lags)? Leads can be used to pull start dates back for successor tasks to maintain finish dates, which can introduce risk into a schedule.
What about the difference between the current duration versus the baseline duration for planned tasks? Is the schedule forecasting efficiencies in the future that have yet to materialize in the past performance? If you have access to multiple copies of the project, you can look at trends in the changes to the schedule to see if things that are being updated are too optimistic.
The missed task metric is an indicator of where to look, but you need to be willing and able to look at it in ways beyond simply the total number at the project level. Looking at missed tasks, through the lens of time enables you to see a lot more about what that metric is telling you. That is true of most schedule metrics.