Run Chart (+Video, +9-Page PDF)
A run chart is a tool used to show a change in a value over a period of time. It depicts a time-ordered series of data plots with time on the X-axis (horizontal) and the value of the data on the Y-axis (vertical).
Run charts are particularly powerful because they showcase changes that otherwise may be too subtle to notice. These changes are, in many cases, linked to abnormal conditions which can be quickly dealt with.
They are also powerful because they can track data in near real time. Most other tools look at information after the fact. Run charts can be appended with the most recent data added to the end of the series. This immediacy leads to rapid problem solving, often before problems grow.
One final benefit of run charts is that most front line leaders are capable of creating and using them to solve problems. The actual gathering of data and updating the run chart takes very little expertise and can be done by most people on front line teams.
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While most problem solving efforts in Lean loosely follow the PDCA cycle, there are a variety of tools you must use within that structure to effectively analyze a problem. The run chart is one such tool. It is extremely valuable in both problem identification and in root cause analysis.
The power of a run chart lies in its visual nature. The impact of a graphical representation of a data series carries a much greater visual impact than a series of numbers.
For example, look at the graph below, and try to quickly identify when changes occurred. Two things should stand out.
The two indicators shown on this graph are the most likely conditions you will see when using a run chart to track a process on an ongoing basis. In a Lean environment, these two indicators are also the most useful. The first highlights abnormal conditions and gives you an opportunity to make a process improvement. The second is a vital part of the PDCA cycle. When making a change you must check to see whether the results are as predicted. A run chart makes it easy to do so.
Run charts are very simple to create and to use. One of the drawbacks of this simplicity is that common-cause variation can look like a change in a process. Every operation has variation to it. Some of that variation is inherent to the system. That is called common-cause variation, or noise.
Think of an icicle melting from your gutter. Most of the drips will fall in a very small area, but they will not be in exactly the same space. That tiny bit of fluctuation happens without any external stimulus. That is common-cause variation.
On the other hand a gust of wind or a large truck driving by or a slamming door can all affect how that drip will fall. That type of variation is known as special cause.
When there is a large degree of variation in the system, common-cause variation can look like a special cause. The result is that a person may spend considerable resources trying to chase down something that does not exist. That’s not to say that you should never go after reducing common-cause variation. It is just important that you know whether you’re trying to make a systemic change, or are trying to fix something that is happening outside of the defined process.
A control chart is like a run chart on steroids. It uses statistics to create control limits that isolate the common-cause variation from the special causes. These take considerable expertise to set up and maintain, though. Because of the costs to set control charts up, they are typically used sparingly and in situations where the cost of failure is high.
Fortunately, in most cases a run chart will be sufficient for your needs. Combine that with the fact that run charts can be set up by people at all levels, and you have a very powerful Lean tool.
As mentioned earlier, the occasional blip on a run chart is often a result of common-cause variation. Significant spikes, however, should be looked into.
In addition to the obvious outliers, there are several other patterns to watch for on your run charts.
On occasion, you will be asked to update run charts. If nothing is done with the data you collect it can be very frustrating. If you are lucky, though, the run chart will lead to assistance in solving problems.
Sometimes, you will need to nudge the continuous improvement process along. Learn to identify the indicators on a run chart. You can even note the problems that you find directly on the chart. More importantly though, when you do see a problem, get the ball rolling. Try to identify the root cause or at least gather more information that can help with that analysis.
The more involved you are in the follow-up to problems the run chart uncovers, the more likely you are to see positive change.
Like all data collection efforts, be sure to do something with the information you gather. Few things are as frustrating for a team member as collecting data for no reason.
Fortunately though, run charts provide information that is hard to ignore. When you see the highly visual issues that show up on this problem-solving tool, it becomes a conscious choice not to act. Run charts peel back the excuse of ignorance.
One good way to make sure run charts are acted upon is to post them publicly. It is easy to ignore a run chart that is sitting in the bottom of a desk drawer. A run chart posted on a wall demands attention.
One thing to consider before you start collecting data, though, is whether you have the resources to do something about the problems you uncover. Think a few steps down the road. If you are limited in your continuous improvement resources, focus your efforts on just a few areas. As you free up more time through productivity increases, you will be able to expand the scope of what you monitor.
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