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Math Help - Interpolation

  1. #1
    Super Member Quacky's Avatar
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    Interpolation

    How would I use interpolation to find an estimate of the median and quartiles of a frequency distribution?

    I've always struggled with statistics.
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  2. #2
    Super Member Quacky's Avatar
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    I'm sort of alright with the median, it's the quartiles which I get wrong.
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  3. #3
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    The first quartile is where 25% of the data is less than or equal to the number and the third quartile is where 75% of the data is less than or equal to the number. I'm not sure what you mean by "interpolation". If you are saying that, say, the 25% point lies between two data points, taking halfway between is perfectly valid.
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  4. #4
    Super Member Quacky's Avatar
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    Interpolation - just a weird word?

    I copied that word from an example question. Essentially, the question gave a distribution such as the one below, and asked me to 'using interpolation, estimate the values of the quartiles' I know that the lower and upper quartile both have seperate formulae, I just can't remember them and they don't seem to be displayed upon the internet.

    Interval Frequency
    00<x<05 6
    06<x<10 10
    11<x<20 12
    21<x<35 4
    35<x<40 2

    Which is an example I've made up off of the top of my head, how would I estimate the quartiles without drawing a cumulative frequency graph or the like?
    Last edited by Quacky; February 9th 2010 at 02:18 PM.
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