Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Brain cramp on this averaging

  1. Dec 29, 2005 #1


    User Avatar
    Gold Member

    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

    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


    User Avatar
    Science Advisor

    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


    User Avatar
    Homework Helper
    Gold Member

    This is where I am confused.

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


    User Avatar
    Gold Member

    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


    User Avatar
    Gold Member



    It's just 357 / 107.

  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


    User Avatar
    Gold Member

    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


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

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

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Brain cramp on this averaging
  1. Strain on Brain (Replies: 2)

  2. Strain on Brain (Replies: 1)

  3. Brain Teaser (Replies: 7)

  4. Brain teaser (Replies: 1)

  5. Brain Teaser (Replies: 6)