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What is Span

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  • #29475

    Dan Hickey
    Participant

    Does anyone have a nice clear and detailed explanation (graphs, powerpoint?) of SPAN that they use to explain the concept and how it works to their customers???

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    #75617

    Farley
    Participant

    I don’t know how it works, and I’m afraid to find out what’s in it, but Spam has been around for ages.  I’ve never seen a Powerpoint presentation on it.  I just take it out of the can, lick the Spam jelly off and go to town.  It makes a great SS training too, “The Uses for Spam”.  Just make sure you don’t limit yourself to edible options.  In a pinch, you can even throw it in a blender and use it for brake fluid.

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    #75619

    Gabriel
    Participant

    Farley: Dan is not asking about “SPAM”, but “SPAN”.

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    #75623

    abasu
    Participant

    There was a thread discussing this topic earlier.  Span can be defined as
    span = (customer WANT date – actual RECIEVE date) for a product or service

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    #75635

    Patrick
    Participant

    From what I’ve gathered over the last little while, span is a metric that is used to measure the ability to meet customer expectations.  You could look at it as range or variance, if you wish.  GE refers to span in their annual report ever since they have become more customer focussed.  For example, if you are to deliver a product on day x, your performance might show a range (or span) of plus or minus 2 days.  The precept is that your customer is not necessarily satisfied until your span is 0.  You can find out more about it by visiting the GE website.

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    #75691

    RR Kunes
    Member

    Another example of a company (GE) creating (complicating) a simple concept.
    This is simply  a measure of the lack of timeliness of a delivery.

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    #75701

    billybob
    Participant

    Spam is the other funny meat..not to confused with my possum meat.
    “Go Red Sox….its the big weekend series against the Yankees”
    Billybob

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    #75704

    keyes
    Participant

    Yes, another metric…
    Span merely tries to describe the variation in delivery.  (just as standard deviation would)
    We currently live and die by the % on-time delivery metric here at company X.
    Does anyone know of other metrics to describe timeliness of delivery  Should we use standard deviation?  As a customer I would rather have my product delivered “early” than “late.  However, we cannot assume that every customer wants everything early if they can get it.  Some customers actually give us a “span” to ship.
    Any thoughts? 
     
     

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    #75715

    Carlos T.
    Participant

    Greg,
    I think you nailed it on the head. The best way of determining the span is by asking the customer what is acceptable for “early” and “late.” By knowing the upper and lower specification limits you can then determine defects and opportunities and calculate the process capability based on continuous data.
    CT

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    #75725

    Patrick
    Participant

    I agree with you but we have to be careful.  As a customer, there are costs associated with both early AND late deliveries.  They are not the same.  Early implies carrying unnecessary inventory and creating opportunities for losses and damages while late invariably implies impact to production…..

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    #75775

    AAA
    Participant

    Span is a measure of range, generally around some target like due date. In some cases it’s the highest value minus the lowest value, or it could be the 95th percentile value minus the 5th percentile value, or some such calculation. It can also be expressed as a ratio of the two numbers.
    For some customers, it doesn’t matter that you did something quickly, just that they received it when they expected to. In order to reduce variation around customer expectations, it is helpful to see how far off from the target you are on a continuous basis rather than how quickly you fulfilled the order.
    In addition to Patrick’s comments about the “evils” of early delivery, if “early” happens frequently enough, it becomes the target in the eyes of the customer.

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    #75804

    Mike Carnell
    Participant

    Patrick,
    You made some very good points. Typically the people who don’t mind it coming in early are the ones that do not understand the cost associated with early arrival. It is a security blanket, just a inventory has always been. It makes the production and puchasing people feel all soft and warm inside to see it sitting there. They don’t pay for the material.
    Late obviously does not work.
    We did this type of thread once before. I didn’t understand then why we needed “span” since we already have range and Standard Deviation. Is it really just the “we are different” mentality. I have never had anyone explain what the advantage of “span” is over the regular measures of dispertion.

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    #75810

    Patrick
    Participant

    Mike, I think you are right; it is a “we are different” mentality.  Or perhaps it is a way to reach people who know little about (or are intimidated by) statistics…
    In their 2001 annual report, GE refers to entire business units reducing their span by 70% (looks good to a layman but doesn’t really say much to me…).
    Patrick

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    #75812

    ktrainn
    Participant

    SPAN is a variation measurement used typically for non-normal distribution’s. First take your data (let’s say delivery data) and subtract each data point from the customers required date, giving you a delta to commit. Next take your data and calculate the 10%, median, and 90%. The SPAN is the difference between your 10% and 90% number. So if you deliver a product 10% of the time 13 days early or earlier (-13 days) from your customers required date and 10% of the time you deliver the product 14 days later or later than your customers required date (+14) then the total SPAN is 27 days (14 – (-13)). Companies target a SPAN of 2-4 days. Also depending on your sample size you can use 10/90 or 5/95 or 1/99 percentiles to measure SPAN. There is an improvement/analysis strategy used to uncover underlying processes that hold the best SPAN it is called segmentation and stratification.
    Hope this answers your question.
    ktrainn

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    #75831

    Mike Carnell
    Participant

    ktrainn,
    I am OK with how it gets calculated – basically it is a truncated range. What I don’t understand, I think Patrick answered it, is why we need to invent a thing called span. Just another iteration of the “we are different” mentality. Dr. Deming documented this mentality 40+ years ago in his Obstacles to improvement and it is alive and well today.
    Thanks for the explanation.

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    #75840

    ktrainn
    Participant

    Point taken. My question though, is what metric do you use to measure the variation in your delivery process? I think this is one of the reasons why SPAN and similar metrics were developed.
    Also Stability Factor = (1st quartile) / (3rd quartile) from a BoxPlot.
    Continuous Metric Improvement, maybe I am wrong though?
    Ktrainn

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    #75843

    Mike Carnell
    Participant

    ktrainn,
    The bottom line is that if  “Span” is working then we really need to leave it alone. It just seems so infantile to have people latch on to a metric that is really just a spinoff of range as long as it has their own name. Seems like a waste of time and effort.
    One of the original advantages that Motorolan’s speak about with the advent of SS was the common language. It seems a little self defeating to bring in dialects such as “Materialese” because the materials/Purchasing function refuses to speak basic stats.
    Thanks.

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    #75849

    PAB
    Participant

    Mike,I think Patrick has the answer.  SPAN is simply an easier way (vs. Variance, or Std Deviation) to get everyone involved; particularly those with less formal academic backgrounds.  As long as it promotes the right behavior – I don’t see anything wrong with it.  The more we make it tangible for people the better off we’ll be.  Ever try improving a delivery process without finding a way to get the warehouse team involved?PAB 

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    #75850

    Patrick
    Participant

    ktrainn,
    In answer to your question…As a customer, I don’t like the span metric because “if it ain’t here when I want it, it’s a defect”.  So I really think that we could look at this from a discrete data perspective and assign a sigma value that way.  It’s harsh but we could always look at the COPQ data afterward to illustrate the need to be “on target” versus “give or take a few” days.  In the automobile industry, we measure deliveries in terms of minutes, and the penalties are severe….
    Cheers,
    Patrick 

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    #75853

    PAB
    Participant

    Mike,
    SPAN is simply an easier way (vs. Variance, or Std Deviation) to get everyone involved; particularly those with less formal academic backgrounds.  As long as it promotes the right behavior – I don’t see anything wrong with it.  The more we make it tangible for people the better off we’ll be.  Ever try improving a delivery process without finding a way to get the warehouse team involved?
    PAB

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    #75875

    Leung
    Participant

    I seems to me that it is important to use the metrics that people are comfortable with (as long as there is some rationale behind them). My job is to encourage the use of the metrics to continuously improve.
    With time, you can usually help a few people move to more statistically sophisticated techniques. But please realize that, for most people, standard deviation is a very statistically sophisticated concept.
    My 2 cents.

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