Let's say you're using a machine to fill containers with a liquid product, you want to analyze the full volume of data of this liquid product. This you collect a random sample of 10 containers. before you proceed with the analysis, you need to identify if the captured data is stable or unstable. This is an interesting example. You want to identify if the collected data is stable. Rank chart is a tool that will come in handy to identify the stability of this data.

Rank chart helps you identify patterns in your process data. It plots all of the individual observations. It also draws a horizontal reference line at the median. The non random or unstable behavior in your data is detected by observing trends, oscillations mixtures clusters in the output of the ranch chart. Such patterns suggest that the variation observed is due to special causes. A few key points to note are an important component of a ranch chart is called us subgroups.

If you are new to this concept, please review the material that I have added in the resources section of this lecture. It will provide you all the details on this topic of subgroups. When can you use a rank chart? Since a rank chart helps you identify the data stability, it is advisable to use this chart at the beginning of any analysis. And unstable data does not point your analysis to the right root causes. However, if your data is stable, it will indeed highlight the right root causes.