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Too many zeroes

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  • This topic has 4 replies, 3 voices, and was last updated 10 years ago by J.
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  • #26874

    ZeroHero
    Member

    How do I analyze attribute count data when majority of my counts are zero?

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    #65331

    Remi
    Participant

    Hi ZH,
    see articles on G-control Chart (search Main page)
    Other option is: define 2 CTQ’s.
    CTQ1= % of non-zero’s over longer time period; and treat it as you would reject level (no USL, LB=T=0)CTQ2= count (or %) if >0 over the time/amount already chosen and analyse this as reject level.Both together give an indication of quality. Danger is in analysing CTQ2 over time because of gaps in time axis (each time there was a 0 in your original data).
    Remi

    0
    #65356

    J
    Member

    Hi Remi,
    I am working on having a control chart for Defect density and I have a similar problem of having defect data with too many zeros.
    What I understand from your reply is to plot non-zero points separately in control chart & For zero data points, use % of non-zero in G-chart. However I am not very clear with CTQ1(the % of non-zero part). Can you give more details on this ?
    I am doing this as part of software process improvement in CMMI & not fully familar with six sigma concepts like CTQ. So I would appreciate if you can explain in simple terms.
    Thanks
    Sri

    0
    #65357

    Remi
    Participant

    Hai Sri,
    No problem; I am not an IT expert so don’t know what CMMI is.CTQ can be translated into ‘variable that is important to measure’. It generally is a parameter of which your customer has decided that it is important to know what it is doing.
    Explanation by example.
    I want to measure Delays.Each time there is a delay I record the # of (micro)seconds of delay; when there is no delay the recorded result is 0. Values smaller than 0 are not expected.
    I will see two groups of data: group1 where there is no delay (the 0’s) and group2 where there is a delay (values greater than 0). The better my process is the more data will be in group1 instead of group2.
    As quality measurement I can evaluate what is happening inside group2 and try to improve the amount of delay (reduce the mean delay time). So I improve INSIDE group2. (CTQ2)
    Inside group1 I have no info (all values 0). So I cannot improve there (and no need). But what I can try is to change the sizes of both groups relative to each other (improve such that more products become of group1 instead of group2). This is what I mean with CTQ1. So my parameter I measure is over a certain time period the Size of Group1 (and or group2). So for each time period “# datapoints in group2″/ “data points total” would be also a measurement for my quality. And this measurement can not be smaller than 0 (LB= Lowerbound=0). But also my Target would be 0 (I want no delays at all). But maybe for your project you would choose a small value instead because ‘no delays at all’ is not possible. You customer generally will not want to give you an upper spec on delays (USL) because if he did he would tell you that any delay smaller than that USL would be acceptable.
    Does this help you?
     
    Remi

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    #65358

    J
    Member

    Thanks Remi for the quick and clear response. I will figure out how to fit in for my requirement.
    Regards,
    Sri

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