About Run Charts and Indicators
If you are reading this article you probably already know the importance of tracking certain metrics, known as performance indicators or even key performance indicators (KPIs), to understand how your business is performing. Tracking indicators over time allows you not only to view the random variation in your data but also to watch for trends or other signs that performance of a process or set of processes is changing.
In Six Sigma, the tool of choice for viewing data over time is usually the control chart. However its simpler cousin, the time plot or run chart, provides much of the same information and can be easier to explain to employees and other business leaders.
A run chart looks similar to a control chart but does not include the control limits. It does include all the data points along with a line representing the average, known as the center line, and any signals of special cause. It will not display outliers as does a control chart, but all the other special cause tests can be run and displayed using a run chart.
Many programs used by Six Sigma practitioners, such as Minitab or the Excel plug-in QI Macros, can easily create run charts from your data. These programs have options you can set to choose the mean or median as the average, to select which special causes to test for, and more. Or read our article on creating a run chart in Excel.
As for a control chart, the data for a run chart may be continuous. Numerical data that measures a physical characteristic or any other variable that can take any value along a continuum is known as continuous data. It includes common indicators such as revenue, cost per unit, cycle time, and widget length. Attribute percentage data and some attribute count data may also be appropriate for a run chart. (Read our article on data types if you need a refresher.) In most cases it will be obvious whether your data is appropriate for a run chart, and if you have the wrong type it will simply not make sense. Check with your Master Black Belt or other leader if you need guidance.