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Best Measure of Variation in Data Sets?

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  • #249886

    Jamessmith
    Participant

    Does anyone know what the best measure of variation/consistency is when trying to predict the metric into the future? For example, if I’m looking at the variation of growth in something of the variation of a certain stable percentage, what should I use? There are so many but I don’t fully understand the advantages and disadvantages of each one, but for example coefficient of determination is bad at determining a data set that you want stable and coefficient of variation is bad at determining a slope in a data set. What should I use? Your help would be a lifesaver.

    • This topic was modified 2 months, 3 weeks ago by Jamessmith.
    • This topic was modified 2 months, 3 weeks ago by Katie Barry.
    • This topic was modified 2 months, 3 weeks ago by Katie Barry.
    • This topic was modified 2 months, 3 weeks ago by Katie Barry.
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    #249895

    Robert Butler
    Participant

    I might be missing something but, as written, your post appears to be expressing two different requirements.  You say you want to predict variation, specifically predict variation trending, however, the examples you give have nothing to do with prediction.  Both both CD and CV are strictly summations of current affairs – they don’t have any predictive capabilities.

    For prediction you would need some kind of equation which would relate your process inputs to variation output.  It is possible to build such an item but the effort/cost involved would be substantial.   What you can do is run an experimental design on your process and then analyze the results using the Box-Meyer’s method to identify those variables that are significantly impacting your variation.  Armed with the results of that analysis you could construct a predictive equation for variation change.

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    #249898

    Jamessmith
    Participant

    Thanks for answering, and I get what you’re saying. The things is that I am trying to predict if the future of a metric will behave similar to current affairs, and I wanted to use the consistency of some metric as the signal if it would. I was looking for some current affairs metric that can tell me if something like the historical average growth rate will continue or if a certain ratio will stay stable in the future. But if not what do you think is a better calculation to predict the future?

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    #249922

    Robert Butler
    Participant

    The short answer to you second post is: there’s nothing like that out there.

    Let’s take another look at what you are asking:

    You said: “I was looking for some current affairs metric that can tell me if something like the historical average growth rate will continue or if a certain ratio will stay stable in the future.”

    If a measurement such as you are requesting existed, the folks who buy and sell stocks would all be multi-billionaires because they would know with certainty which stock was going to do well forever and conversely. This is the reason you will find the following line in every stock offering prospectus:

    “Past performance is no guarantee of future results.”

    The best you can do is analyze data with an eye to identifying process characteristics that will adversely impact your process average growth/stability and, once you have identified those variables, put in place process elements that will minimize/eliminate their adverse impact.  Such an approach should give you some measure of growth rate maintenance/ratio stability for some period of time but not for all time. This is because there is no guarantee those variables you have identified and are controlling are the only variables (both now and in the future) which have a significant impact on your process.

     

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    #249961

    Jamessmith
    Participant

    No, you’re absolutely right. My problem was that I’m looking for some metric that  shows the level of consistency if some historical trend line. I have been using CV and CD but CV by itself doesn’t look for a trend, just the consistency, while CD doesn’t seem to be able to measure a stable trend line. I wanted to know what would be the best metric to detect the consistency of a trend line, for example if I was trying to find the consistency of some species exponential growth or if I was looking at extraneous factors influencing the ratio from predators to prey in the region. I just wanted to sharpen up my current consistency  measuring strategies to something a bit more sophisticated.

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    #250028

    Robert Butler
    Participant

    I’ve been giving your problem some thought and I can’t think of any single statistic that will capture consistency both with respect to stability of system variability and constancy of trending.  The issue you are facing is that of an evolution of both variation and trend across time. As far as I know, if time is involved you will have to take it into account which means you will have to do more than examine simple population statistics.  All of the methods I know for tracking consistency of variation and trend across time require graphs and regression/time series analysis.

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    #250073

    Jamessmith
    Participant

    Okay, thanks for your help. What I have been doing is using the coefficant of correlation on the list of numbers and depending on the level of correlation I will use either the coefficient of determination or coefficant of variance to determine consistency. Thanks again for your help and have a great day.

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