What is Average Run Length & Average Production Length when used in Control Charts?

T

tahashamim

Hi,

As I am trying to understand Average Run Length, Average Production Length term came in a book and did not give any details. Does any one have detail material or even an introductory level information on it besides a definition?

Taha.

W

wmarhel

Re: Average Production Length

Hi,

As I am trying to understand Average Run Length, Average Production Length term came in a book and did not give any details. Does any one have detail material or even an introductory level information on it besides a definition?

Taha.
Without knowing the book, or the context in which the term was used makes it a little tough. I would look at "Average Run Length" as being a function of time: minutes, hours, days, etc. This would then be the average amount of time that a particular part is in production. If you always started a part on a Monday and ended on a Friday, then your average run length would be five days.

This term could also apply to a process type of product such as wire or steel coils. For this example if you had production runs of 100ft., 200ft and 300ft.; your average run length would 200ft. So context is critical.

Wayne

harry

Super Moderator
Re: Average Production Length

I am having the same question marks as Wayne above. The context is very important. Are you asking this question in the same 'context' as the other question you asked in another thread:

2- Is the average run length performance of a control chart a more meaningful measure of performance than the type I and type II error probabilities? What information does ARL convey that the statistical error probabilities do not?

T

tahashamim

Re: Average Production Length

Sorry for the confusion. Yes, Average Production Length and Average Run Length - both in the context in using control charts.

So as they say ARL = 1/p = for a process in which mean has not shifted, ARL = 370 sample - a false alarm may come after the 370th sample.

They the author mentioned that ARL is not so good as this has a wide standard deviation and one should use Average Production Length. Interestingly, the author said APL will also have wide standard deviation as it is linked with ARL...

So I thought regardless of APL link with ARL, it has a good information because it can give us number of units produced potentially that has mean shifted... Hence I was looking for more details on APL such as its formula and its application if possible.

If it is still not clear, I can scan a page in which author mentioned it hoping this is not against copy right.

thanks,
taha

Steve Prevette

Deming Disciple
Staff member
Super Moderator
Re: What is Average Run Length & Average Production Length when used in Control Chart

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