Metrics Quality Systems/Processes/Improvement

There is a wide variety of ways to display data for an Instrument Panel, but line and bar charts are straightforward, easy-to-understand tools for organizations that aren’t accustomed to using charts and graphs to help manage and make decisions. They are also the two most common charts on our client’s Instrument Panels.

So, since we are currently working on our Instrument Panel process, we thought we would share in our blog the distinctions we make with clients on these two common charts. How you choose to display your data depends on what you want it to show you. We have included a brief look at the key points of these 2 common charts below.

Line Chart

What line charts show best:

  • Data over a period of time, i.e., continuous data or sequenced data. Line charts are often used to compare changes over time between two groups, like the number of new customers and number of returning customers over the last 2 years.
  • Variation – both the normal range in which data is expected to fluctuate over time (common cause variation) and outlying data points that merit investigating (special cause variation)
  • Trends and patterns
  • System changes – when the measure shows a complete shift to a different level


basic line chart

The above chart shows water usage for a family for two years. Because water usage changes slightly each month, the line shows variation.  Common cause variation would include things like watering the lawn during summer months, houseguests, etc.  The special cause variation in July would warrant investigating – what was the cause?  A leak in the system would require action while filling a swimming pool is a one-time, explainable event.  The system change could be the result of installing water-saving appliances.

The same theory and thinking should be applied to a line chart in an organization.  What is the cause of an outlying point?  Do we need to make changes in our systems so that the data overall improves?  These are the types of questions you ask when analyzing a line chart.

Bar Charts

A bar chart shows:

  • A comparison of categories at a specific point in time. For example, the sales per region for a given month or the example below, traffic violations in June.
basic bar chart
  • Like line charts, bar charts can also be used to track changes over time. For example, sales for a specific region each month for the last year.
bar chart over time

Choosing your charts

Both a line and a bar chart are valuable for displaying data and effectively to showing valuable information about an organization. Selecting which to use depends on how you plan to analyze the chart and what questions you are needing the data to answer. Create the charts that help you answer questions and better manage the organization today.  Then you can make revisions as you begin to use the tool. A good Instrument Panel is one that is revised and restructured over time so that it continues to provide accurate and useful information about the organization each month.