Capability Statistics - Cp/Cpk vs Pp/Ppk and Sigma level

There's a lot of confusion about capability statistics, here is my take on them...if you have any positive comments to increase our understanding, please leave a comment....
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[quality_bus]

Dear Paul. Of all the videos I've watched so far, this one has helped me the most and reminded me of checking on the basics from time to time. Thanks a lot.

[ZenS]

Great explanation. Currently no available training at my employer. As a budding engineer and new to SPC this is super helpful. Thanks mate!

[jeffreychang]

Preparing for an interview in 2 days, this was a great explanation of the difference between cp/cpk and pp/ppk. Thank you!

[serkanaygun]

Needless to say how much valuable your videos are. Thanks!

[deanopenn]

Hi Paul, Another comment on your videos haha. i have seen a scenario where If PP and PPK fail to achieve the minimum requirement e.g. 1.67 but CP and CPK passes. The big factor is the tolerance is so small it doesn't leave much room for any process variation as PP and PPK is long term. What are your thoughts on this due to tight tolerances?

[johnHiggins-jl]

Hi Paul, great videos as usual which gets us all to think more deeply. Here are my pennies worth. Surely the overall objective is to get CPK and PPK to equate to 1.33 or higher. This implies getting the short-term variability to be the same as long term variability. This also implies getting the within (short term) to equate to the in between variability (long term). Achieving this status implies reducing the overall variability because overall variability is equal to short term plus long-term variability i.e., the square root of their average squares of the short- and long-term variability.

[dianas]

this is wonderful. I work for a large medical device company and we overuse CpK all of the time instead of using PpK. I wil share this video!

[geraintjones]

Thanks for the video Paul, I notice that you don't mention control prior to using the indexes. In actual fact, when the process is in control the indexes will all be the same. I understand the need to get a quick sighting and a commonsense view of the leeway, I also understand that if you sample for a longer or shorter period you will expose different variables. You mentioned about predictability but you will not be able to achieve that without stability in the process, the quicker you get to work on this the quicker you can enjoy the day to day predictability.

The way we compute the indexes is irrelevant if the process is in control and that's where we need to get to isnt it?

Its true to say that if I had a flow chart for the use of these and I just went ahead and computed the Cp and Cpk and these were better than I expected it would give me a warm feeling. If the flow chart directed me to knuckle down and stabilise (assuming I had to) I would agree, if this is what you meant I agree with you. There are lots of people out there comuting the summary stats and "cashing them in" before assessing the behaviour of their process, after all, who wouldn't want to get on with making money by producing. A stable process is quite an achievement and not a natural state to be in.

[josecuencatorres]

extraordinary explanation. Congratulations Paul !!

[naven]

Nice words Paul. Be practical and use your wit. Great way of explaining

[zlatkomatic]

Wow, what a great explanation! I have just became huge fan, thank you for brilliant straight-forward approach to clarify these confusing matters!

[ahmadsafiuddinabdrahim]

Thanks Paul, it helps a lot to understand the differences between cp/cpk, pp/ppk, cm/cmk. I thought that If the samples is less than 50 we call it pp/ppk, >50 is for cp/cpk. I was wrong, not only me but the entire organization. :P

[MA-jxum]

Really like your videos, thankyou. I used to visit heat treatment suppliers, who didn't apply SPC to time and temp processes for multiple parts in ovens, saying it wouldn't benefit them, have you got a comment on this and if possible refer me to another you tube video of yours.
Additionally do you do a version SPC for senior leaders quoting examples of successful applications in industry.
Many thanks

[varunn]

Hello Paul, one of best explanations for Cpk and Ppk. Though I have a query1. Is there any difference in way of data collection in Cpk and Ppk 2.Any difference in way calculation of mean in both process

[letslearntogether]

Sir, Please share any video on cost of poor quality, PEST analysis, SWOT, Cost benefits analysis, Balance scorecard.

[suvatmg]

Hi Paul, really appreciate your video series. I have few questions if you could kindly help me understand.
1. For a sample size of 4 would Shewhart constant be 2.0588? I can see d2 value increases as you increase sample size. how does this affect Cpk?
2. If Ppk takes wider standard deviation, would ppk give better indication of process capability if used for small sample sizes?

Thanking you in advance.

[VsOct]

Very well explained, with practical application. Thank you!

[andrewrivett]

Thanks Paul - I like your explanations

[anonmortal]

Great explanation and nice Les Paul, lefty.

[giuliabartolini]

Hi Paul, very good explanation! I always got it wrong. Anyway, I have one question: how can we modify the number of data collected when we have low volumes (for example 100 parts per year)?