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Brain cramp on this averaging

  1. Dec 29, 2005 #1

    DaveC426913

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    My website posts my movie reviews and rates them from 1 - 5. I want to post an average*, and I can't figure out how to do it.

    Rating Number of movies
    1.............6
    2............10
    3............41
    4............37
    5............12

    I can't figure out how to average* them without biasing them in favour of the higher numbers.

    (*by average, I mean I should get approx 3.? / 5 .)
     
  2. jcsd
  3. Dec 29, 2005 #2
    When I average them out I get about 3.36 which I would think is approximately 3.
     
  4. Dec 29, 2005 #3

    krab

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    dunno why this is a problem. avg. is
    [tex]\overline{s}=\sum n_is_i/\sum n_i[/tex]
    This doesn't "bias" to high scores: consider if you had 6 1's and 6 5's and nothing else. You would get avg.=(1*6+5*6)/(1+5)=3 exactly as expected, so what do you mean by this "bias"?
     
  5. Dec 29, 2005 #4

    JasonRox

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    This is where I am confused.

    What do you mean by "bias"?
     
  6. Dec 29, 2005 #5

    DaveC426913

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    OK, so


    (5*12)+(4*37)+(3*41)+(2+10)+(1*6) = 357
    1+2+3+4+5 = 15

    357/15 = 23.8
     
  7. Dec 29, 2005 #6

    DaveC426913

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    Oh.

    Oh.

    It's just 357 / 107.

    Duh.
     
  8. Dec 29, 2005 #7
    Don't divide by the sum of the "choices" divide by the number of total ratings

    ie. ((6*1)+(10*2)+(41*3)+(37*4)+(12*5))/(6+10+41+37+12) which is about 3.36
     
  9. Dec 29, 2005 #8

    DaveC426913

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    I've had it right all along and I keep second-guesing my code. (This is not even the first time I've tried to "fix" it.)

    It's been saying 3.3 for a long time now, but that's not because it's "stuck" or broken, that's because 3.3 *is* the point of convergence, and subsequent entries are strongly averaging around it.

    BTW, for those interested, my reviews and ratings page is here. It is database driven, and I am rather proud of it.
     
  10. Dec 30, 2005 #9

    Integral

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    I have split off the movie disscussion to a thread in GD call Movies here

    Integral
     
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