The difference between run charts and control charts

Steve DaumA customer recently asked one of our support representatives the following questions: What is the difference between a run chart and a control chart? And when should I use one vs. the other? These are great questions because they allow us to highlight some of the benefits of control charts.

When you create any chart, you are typically trying to answer a question. For example, you might be asking, “Has my process improved?” or, “Has my process gotten worse?”  You might be asking, “How is the process running today compared to yesterday?” Before you decide on using a run chart or a control chart, consider the type of question you want to answer.

A run chart is the simplest of charts. It is a single line plotting some value over time. A run chart can help you spot upward and downward trends and it can show you a general picture of a process.

A control chart also plots a single line of data over time. However, control charts include upper and lower control limit lines with a centerline. These lines are calculated based on the data being plotted, and this allows you to answer more questions about the process. For example, you can ask the question, “Is my process stable or in control?” If any of your data is outside the limit lines, the answer is, “No. Your process is not stable.” You would then know that system changes may be required to make it stable.

Control charts are designed to prevent two common mistakes: 1) adjusting the process when it should be left alone; and 2) ignoring the process when it may need to be adjusted. Run charts lack the benefit of statistical control limits. So, if they are used to adjust your process, this may add more variation to the process instead of reducing the variation.

Both run charts and control charts are helpful, but depending on your goals, control charts generally provide more specific information and insight into your process.

15 thoughts on “The difference between run charts and control charts

  1. Pingback: W17_EDN_Run Chart | Casablanca Q1-2012 AACE

  2. I want to know the interpretation conditions and which one is preferaable on mfg line run chart or Control chart

  3. I suggest that a control chart will give you more information – for a manufacturing line – than a run chart. However, the control chart does require more up front thinking and setup. For example, you need to establish the control limits and out-of-control test rules you will use. Regarding interpretation – with a control chart, you look for signals that something has changed; something that might be explained. This would be data points beyond the control limits or runs of 7 above or below the mean – or trends of 7 points increasing or decreasing. Often people will start with a run chart – just to create a “visual” for the process – and later transition to a control chart. You might watch this short video about control charts:

    • Hi Jonty,

      A Pareto chart is a bar chart for ranking aspects of a problem. Typically, a few aspects make up a significant portion of the problem while many trivial aspects exist.

      A control chart is a graphical representation of a characteristic of a process, showing plotted values of some statistic, a central line, and one or two control limits. It is used to determine whether a process has been operating in statistical control and is an aid to maintaining statistical control.

      Please visit our Quality Advisor section to learn more:

  4. What is the role of run chart, pareto chart, scatter diagramm, control chart in CAPA action? which one is more applicable?

  5. sometimes we use control chart with data that has an upper limit but it has no lower limit or the lower limit has no meaning. is that also considered a control chart?
    thank you

  6. I am managing an inbound call center quality, please suggest what is more useful for my process- Run chart or Control Chart ? How about I-MR chart ?

    • Hi Ankita..
      If you have data of any sense like shift wise, day wise, person wise etc.. with time interval (other event will happen ) then IMR chart will be useful in that case.
      Suppose in case of call center you have to calculate a feedback of person who attended the customers call in a particular shift with event such as tea break, lunch break n many more events you have to go for IMR chart.

  7. Hi, i am assembly some bought out parts in my product. Bought out parts are manufactured with all controls at supplier end. I am assembly those parts on my product and measuring efforts on FG part. Kindly suggest –
    1) Can i conduct SPC for efforts measured on bought out parts?
    2) Which chart i should prefer? (Control chart (X bar & R chart or any other run chart)

  8. Which of the Run chart and Control chart answers the question – Is the process stable or not? Secondly, can a process be stable but out of control? Are Stability and Under control, 2 different terms or can be used interchangeably?

  9. Use the control chart when you want to asses stability. Yes, stability and control are often used interchangeably. By out-of-control, we mean that data from the process, shows out-of-control conditions when plotted on a control chart. Conditions such as points beyond the control limits, runs above or below the mean, and trends moving up or down. When these are present, it generally means the process is not stable or not predictable. Note that the world is full of “unstable” processes.

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