Is there a term that indicates a data that has fallen outside CL/SL for Statistical Process Control?

Most seem to call it simply "Data out of bounds of CL/SL" but I'd like to know if there's a specific term for it.

  • $\begingroup$ Sometimes, it might be called 'a signal'. e.g. see here. $\endgroup$
    – Glen_b
    Jun 27, 2013 at 1:34
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    $\begingroup$ A term I have often seen, and grew familiar with decades ago (when I was writing control chart software), is "OOC": out of control. See, for instance, books.google.com/…. $\endgroup$
    – whuber
    Jun 27, 2013 at 15:02

1 Answer 1


There's no commonly accepted term for this condition other than "outside of control limits".

There is a term that is used when the data falls inside the control limits. That term is "in control", or "in statistical control". As you would expect, the opposite of "in control" would normally be the term "out of control", however that implies far more than simply being outside of the control limits. So, a typical Controls Engineer knows what you mean by "outside of control limits".

Here's a link to a typical control chart (about one third of the way down the page).

  • $\begingroup$ Thanks for the clarification. One of the comment says that it's sometimes called a signal. Is it appropriate to use the term signal in this context? Or am I forced to use "outside of control limits"? I'm asking because I'm designing an SPC application and the spaces are limited for labels, so I'd like to keep the terms as compacted as possible while not making it dubious. $\endgroup$
    – TtT23
    Jun 27, 2013 at 2:48
  • $\begingroup$ The term "signal" as described in that link is not a formal definition. That link simply says that any data point outside of a control limit is a signal or indication that something statistically important is taking place. $\endgroup$
    – bill_080
    Jun 27, 2013 at 2:56
  • $\begingroup$ In terms of labels, the only label that might be useful is "in control" when the data is inside the control limits, but even that might be considered overkill. I've looked at a lot of control charts and I've never seen the "outside of control limit" region or "in control" region labelled. But, I have seen them shown in different colors (red for outside of the control limits). $\endgroup$
    – bill_080
    Jun 27, 2013 at 3:02

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