Why does ControlChart uses standard error

Matlab's control charts plot the upper and lower control limits using standard error, instead of standard deviation.

However, it looks like the usual method is to use standard deviation.

Why does Matlab use standard error and is there a way to use standard deviation instead of standard error to plot the control limits?

Answer 1

[Samay Sagar]

Hi @Jimmy Zhan

In MATLAB R2024b, you can specify the control limits using the "Limits" input field. You can calculate the standard deviation using "std" function and then assign the control limits as follows:

myControlLimits = [1 0 2]; % specify limits based on standard deviation here
controlchart(X,ChartType=["i","mr"],Width=2,Limits=myControlLimits) % where X is the measurements data

While the MathWorks documentation do not state that standard error is used to estimate control limits of "controlchart", you can use standard deviation to specify the control limits.

For more information about "controlchart" and "std", you can refer the following documentation:

• https://www.mathworks.com/help/releases/R2024b/stats/controlchart.html
• https://www.mathworks.com/help/releases/R2024b/matlab/ref/double.std.html