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CP in minitab

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  • #51038

    Silu
    Member

    Hi everyone,
    I am working on a project to improve the total process time for each single client request. and I am focusing on the last 12 month data which shows how many days took to complete each single request.
    The objective is to reduce the processing time (from getting the request till final delivery) is 10 days. Our average is 150 days now !!!
    I’ve used minitab and have 25000 requests delivered for the last 12 month, interestingly minitab shows CP=250, and I have a wide range of processing time between 1 day to 500 days.
    does than mean that I have put my effort to use Lean tools to just shift the average processing time, and should not be worry about the STD?
    Also, when I group data instead of one to 20, minitab gives me CP=3.99, I am not sure what number of sample group I have to use in minitab.
     

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    #176295

    Ken Feldman
    Participant

    As in some recent posts, you are trying to do a capability analysis on time.  As you would expect, the data will be skewed and therefore a capability analysis using an underlying assumption of normality will give you meaningless results.  The first step is to see if you can understand the process and possibly stratify your times by some factor.  Why do you have some jobs at 500 and some at 1?  The average might be meaningless if the distribution is really skewed.  The median time might be more useful.  You are just pushing buttons at this point so your results are garbage.  For subgrouping, you would group by some rational subgroup.  Did you capture 5 data points per week?  That would be a subgroup of 5.  The subgroup is used to determine the within group s.d. and is used for the Cp/Cpk measures.  The overall s.d. is used for the Pp/Ppk values.  At this point, you are a good distance away from using Mini.  Make some decisions regarding your data before you start confusing yourself.  If you want to send me the data, I can take a look and offer some thoughts.  drdart[email protected]

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    #176303

    Silu
    Member

    Thanks for your reply,
    Unlike manufacturing, when we get a big order, we push all of them into our process and clock start ticking. Imagine when we have an order of 10,000 requests, the first one will pass in minutes, the request #10,000 could wait for few months! It gets worst when other client have only one request and we don’t have a clear guideline, do we have to tell them it will take 200 days or delay the big request and do the never ending small requests first.
    Instead of using problematic processing time as metric for project sucess I can use delevery on time %. We are very low on that, but since this is the first Lean Sig Sigma improvement project in our company I don’t want to promiss 6Sigma quality right up front, I am a bit conservative. 
    I need my supervisor approval for sending you the data, to make sure there is no confidentiality issue.
    Regards

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    #176304

    Savage
    Participant

    everything is a process – regardless of whether its manufacturing or transactional and therefore lean can be applied to all processes. You really need to understand your takt time first and then establish baselines (where did the 10 days come drom – what is your customer demand rate, you processed 250,000 requests from last year however how many requests were received in total, how many shifts dou you work, how many people per shift, etc),  Six Sigma is great to eliminate variation however you need lean tools to eliminate waste first & the go after the variation with Six Sigma.
    Matt

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    #176305

    Savage
    Participant

    Re-submitted by Matt – noticed some typos!
    Everything is a process – regardless of whether its manufacturing or transactional and therefore Lean can be applied to all processes. You really need to understand your TAKT time first and then establish baselines (where did the 10 days come from? what is your customer demand rate? you processed 250,000 requests from last year however how many requests were received in total, lasy year? how many shifts do you work? how many hours per shif? how many people per shift? etc). 
    Six Sigma is great toolbox to eliminate variation however you need Lean tools to highlight & eliminate waste first & then you go after the variation with Six Sigma tools.
    Please feel free to send me these details on: [email protected]
    Matt

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