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Histogram

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  • January 15, 2007 at 8:37 pm #45824

    Bonnie
    ★ 10 Years ★
    Participant

    Hi,
    Could some body explain how to calculate the bin size (class interval) for constructing a histogram.
    Thanks in advance for your kind help.
    Warm Regards,
    Bon

    0
    January 15, 2007 at 8:57 pm #150593

    qualitycolorado
    ★ 10 Years ★
    Participant

    Bonnie, Hello!Thanks for your posting. This thread from a few years ago covers this material, I think — see what you think:https://www.isixsigma.com/library/forum/c031022_number_bins_histogram.aspBest regards,QualityColorado

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    January 15, 2007 at 9:08 pm #150595

    Atkins
    ★ 10 Years ★
    Participant

    I usually take the range of the data and divide by 10 (cells).  The I take whatever the interval came up to be and round it off to something that will give me reasonable cell intervals (e.g., whole numbers in an ideal world).  The actual number of cells then is whatever that rounded number turns out to create.

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    January 15, 2007 at 9:09 pm #150596

    Atkins
    ★ 10 Years ★
    Participant

    I usually take the range of the data and divide by 10 (cells).  The I take whatever the interval came up to be and round it off to something that will give me reasonable cell intervals (e.g., whole numbers in an ideal world).  The actual number of cells then is whatever that rounded number turns out to create.

    0
    January 15, 2007 at 10:16 pm #150602

    Theo
    ★ 10 Years ★
    Member

    It is refreshing to see you are plotting manually.  You will learn more this way rather than blindly using software like most people.  Software can very much lead people astray, such as the idiotic normal distributions I see plotted over so many histograms. 
    Data Points   Bins
    50-100          6-10
    100-250        7-12
    >250              10-20
     

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    January 15, 2007 at 10:25 pm #150604

    Mikel
    ★ 10 Years ★
    Member

    Manually plotting histograms with an arbitrarily picked number of bins can very much lead people astray. You can create things that look like probelms with the data when no problem exists and you can visully hide things. Much worse than a little curve that is meant as a reference not a test.
    Do you think that just because the guy wants to know how to do bins, he is plotting manually? He is trying to use Excel.  Go create a histogram with Excel and see how the labels do not correspond to the data. Pretty idiotic.to use such functionality when so much better help is out there.
    By the way the advice on bins is =sqrt(n) and adjust slightly to make logical bins.

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    January 18, 2007 at 12:59 pm #150729

    bstout
    ★ 10 Years ★
    Participant

    There is a very general rule called Sturgis’ or Sturges’ Rule with the following formula:
    (Maximum value minus minimum value) divided by (1+3.322*log(n)) where n is the count of the number of observations.  If you round this number it represents a fair approximation of bin size.  This formula attempts to give as close to a normal distribution as the raw data will allow.  You can then use the frequency  function in Excel to create bins and categorize the data by bin.
    Hope this helps.
    Bill

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    January 18, 2007 at 8:16 pm #150759

    Bonnie
    ★ 10 Years ★
    Participant

    Thanks Bill,
    Something like this is what I was looking for. This really helped.
    Cheers,
    Bon

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