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Thread: What does an outlier in a stem and leaf plot look like?

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    What does an outlier in a stem and leaf plot look like?




    I have to analyze some displays (e.g. stem and leaf plot, histogram) I have generated for a homework questions from a group of numbers. I have looked at several textbooks and the internet but I am still having difficulty in finding an example of a stem and leaf plot with an outlier, with an understandable explanation why it is an outlier. If anyone could post a picture of a stem and leaf plot here with an outlier, explaining why it is an outlier, that would be much appreciated. Thanks in advance.

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    Re: What does an outlier in a stem and leaf plot look like?

    http://www.tutorvista.com/q/find-the...am/q4994_87410
    outlier is a value which looks isolated from other values, and it can be either upper or lower end.
    A good stem and leaf plot

    * shows the first digits of the number (thousands, hundreds or tens) as the stem and shows the last digit (ones) as the leaf.
    * usually uses whole numbers. Anything that has a decimal point is rounded to the nearest whole number. For example, test results, speeds, heights, weights, etc.
    * looks like a bar graph when it is turned on its side.
    * shows how the data are spread—that is, highest number, lowest number, most common number and outliers (a number that lies outside the main group of numbers).

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    Re: What does an outlier in a stem and leaf plot look like?

    Quote Originally Posted by SadieKhan View Post
    http://www.tutorvista.com/q/find-the...am/q4994_87410
    outlier is a value which looks isolated from other values, and it can be either upper or lower end.
    A good stem and leaf plot

    * shows the first digits of the number (thousands, hundreds or tens) as the stem and shows the last digit (ones) as the leaf.
    * usually uses whole numbers. Anything that has a decimal point is rounded to the nearest whole number. For example, test results, speeds, heights, weights, etc.
    * looks like a bar graph when it is turned on its side.
    * shows how the data are spread—that is, highest number, lowest number, most common number and outliers (a number that lies outside the main group of numbers).
    Thanks very much, Sadie.

    I understand what an outlier is; I am just having difficulty understanding what it looks like in a stem and leaf plot. Thanks for the example you provided a link to. I would appreciate it if you could clarify a few things I am not sure about. The example states that "In the above data set, 4 is far apart from the other data items... So, 4 is the outlier of the data set"

    My questions:


    How is 4 "apart from the other data items"? Is it because there is a 0 in the stem column?

    When there is a 0 in the stem column, does this mean that there is an outlier?

    Is a 0 the only way that an outlier shows up in a stem and leaf plot?

    Thanks.

    Stem Leaf
    0 4
    2 144457
    3 344455
    4 2344555
    Last edited by alexis2; 12-12-2010 at 01:05 PM. Reason: Amend stem and leaf plot

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    Re: What does an outlier in a stem and leaf plot look like?

    That's actually a misleading stem and leaf plot. They should probably include '1' in the stems even though there is no value that would go in the leaf portion. It makes it more obvious that 4 is an outlier and then the distance between rows corresponds to the same distance for every jump. That's really the reason they call it an outlier. I would say the plot really should look like this:

    Stem Leaf
    0 4
    1
    2 144457
    3 344455
    4 2344555

    Which makes the value of 4 stand out more wouldn't you agree?

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    Re: What does an outlier in a stem and leaf plot look like?

    Quote Originally Posted by Dason View Post
    That's actually a misleading stem and leaf plot. They should probably include '1' in the stems even though there is no value that would go in the leaf portion. It makes it more obvious that 4 is an outlier and then the distance between rows corresponds to the same distance for every jump. That's really the reason they call it an outlier. I would say the plot really should look like this:

    Stem Leaf
    0 4
    1
    2 144457
    3 344455
    4 2344555

    Which makes the value of 4 stand out more wouldn't you agree?
    Thanks, Dason

    It does stand out more as there is no value for leaf when the stem is 1.

    So what actually indicates that there is an outlier in this stem and leaf plot? - the gap in row 1 or the row with a 0 in it? Or both? Is the outlier still 4?

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    Re: What does an outlier in a stem and leaf plot look like?

    This is a stem and leaf plot which I generated. Are there any outliers in this distribution? I am not sure whether the gap (in bold) indicates an outlier or not. If it does, what is the outlier? Any clarification on this/ stem and leaf plot outliers in general would be much appreciated.


    6 : 2
    6 : 899
    7 : 0011123
    7 : 5
    8 :
    8 : 5
    9 : 4
    9 : 566789
    10 : 00000

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    Re: What does an outlier in a stem and leaf plot look like?


    Outliers are a fairly subjective quantity. I would say the most 'unusual' point in that dataset is actually the 85. But would I call it an outlier? Probably not, there's not too much data to go on and it just seems like a bimodal distribution.

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