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Plotting a normal distribution

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  • #45286

    Siegler
    Member

    I’m trying to generate a normal plot of a group of excel values. I used the normdist function to do this. However, I get values over 1 when I do this. any tips on where I am going wrong?

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    #147550

    Lobo
    Participant

    Try Googling “normal probability plots in excel”

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    #147552

    Siegler
    Member

    Google doesn’t answer my question. Is there something specific I am making a mistake with?
    I have a list of values for which I want to plot a normal curve with excel. I calculated the mean and stdev for the set and then used normdist to get the p value to plot. I get values over 1 which is obviously not right.

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    #147556

    Whitehurst
    Participant

    Theres no function that will draw a normal probability plot in excel.
     
     

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    #147557

    Robert Butler
    Participant

    I don’t use Excel for my statistics but based on a quick read of the help section for the NORMDIST function it appears the function will generate random numbers from a normal distribution with mean 0 and standard deviation = 1.  If this is in fact what it is doing then you should get values greater than 1 and less than -1.

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    #147603

    Lee
    Participant

    I too found no canned function, so I made a spreadsheet that accepts values, plots the histogram, provides statistics, and then overlays the normal curve shape over the histogram of plotted points.  It is just part of a worksheet I use to generate SPC charts.  It is not 100% automated, but it beats nothing.
    Contact me offline, at [email protected] if you want to followup.
    Eugene

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    #147608

    Savage
    Participant

    True there is no canned way to plot a normality plot in Excel – unless you purchase one of the many programs that do this.
    Here’s a way to do it though:
    Assumptions:  raw data are in column A and you have n data values.
    1)  Use the RANK function in column B to rank the raw data (use the help to see how to do this)
    2)  Use this expression –>  ((column B-.5)/n)   (this is column C)
    3)  Use the NORMINV function with column C as the probaility.  (this will be column D)
    4) Create a scatter plot with column A as the x-axis and column D as the y-axis. 
     
    Try that and see if that meets your needs.

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    #147624

    BTDT
    Participant

    Siegler:Send me a note at 6SigmaGuru(at)gmail(dot)com and I’ll send you an Excel sheet for the Anderson-Darling test and normal probability plot.Cheers, BTDT

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    #148346

    Vidyadhar
    Member

    Dear Friend,
    There is many more to explore in excel.
    Please try the following path & see whether it satisfy your need or not.
    1. Select Tools manu -> Add-Ins.
    2. One dialog box will appear with many option. Select “Analysis Toolpak”If analysis toolpak is not loaded in your system then ask administator to installed full version of MS-Office.
    3. Again goto “Tools Menu” -> select “Data Analysis” option.
    4. One dialog box will appear with many option. Select “Histogram” to plot histogram & ND curve for your data.
    5. Just follow the instruction appear on the Screen.
    Rgds,
    Vidyadhar.

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    #148347

    Theo
    Member

    Why ??????

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