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Very simple stats question

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  • 30-04-2012 4:31pm
    #1
    lestat21
    Closed Accounts Posts: 221 ✭✭


    Right I know that the answer to this question is probably staring me rite in the face but I just dont understand it....

    When youre getting the interquartile range you need to find Q1 and Q3. If Q1 = n then we use the nth value to find the interquartile range. Simple enough, but if n is a decimal we always round up. Even if n = 2.0001, we round up to n = 3 and use the 3rd value. Whats the deal with that?

    Also if n is a whole number we get the mean of the nth value and the (n+1)th value and your answer is the number used to find the interquartile range. Why cant we just use the whole number? Why do we have to calculate the mean??

    I know this is probably a very basic and simple question, but the process used to find the interquartile range just flies in the face of all the basic arthmetic I know!!!


Comments

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    #2
    TheBody
    Registered Users Posts: 5,619 ✭✭✭TheBody


    Hey op. The interquartile range is the difference between the upper quartile and lower quartile. The lower quartile is the median of the lower half of data and the upper quartile is the median of the upper half. For this reason, it depends on whether you have an even or an odd number of data points. Check out these videos and see if they help.

    http://www.youtube.com/watch?v=DGAXeX42eoE (odd number of data points)

    and

    http://www.youtube.com/watch?v=ZAE-5TJy9kU&feature=fvwrel (even number of data points)


  • Options
    #3
    lestat21
    Closed Accounts Posts: 221 ✭✭lestat21


    Why are they not doing this in any of the project maths books?? Its simpler and shows students exactly where the interquartile range comes from.... Thank you so much!!!!


  • Options
    #4
    TheBody
    Registered Users Posts: 5,619 ✭✭✭TheBody


    They should really do both. If you have a large sample of data, it would probably be easier to use the method you described.


  • Options
    #5
    lestat21
    Closed Accounts Posts: 221 ✭✭lestat21


    True but any method that involved rounding 2.1 up to 3 shouldnt be used in junior cycle as it will confuse students and theyll want to know why theyre rounding up which involves teaching them the first method anyway... Think I'll use this method with junior certs and intro the second method at leaving cert. But I asked a load of teachers bout this and they had difficulty trying to explain it. I also looked online but couldnt find your method of using the median anywhere. Thanks again.


  • Options
    #6
    TheBody
    Registered Users Posts: 5,619 ✭✭✭TheBody


    Glad I could help. A lot of the text books are hit and miss to say the least. I would show them both ways if it was me. The method as shown in the videos I posted above would be the more important in my opinion as it shows what you are actually doing.

    Anyway, I'd encourage you to post here if you are ever in doubt about anything. There are always people here who are glad help out.


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