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Math Help - Hits,ratings & averages

  1. #1
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    Hits,ratings & averages

    Hi there, ive been posting some videos to the metacafe producer awards program. The idea is that you get paid for your video when you hit 20 000 views if your average rating is above 3/5.Each member of metacafe can rate your video out of 5.

    The other night before i went to sleep i checked one of my vids and it was on 15000 views and had an average rating of 4.2/5.

    When i woke up i had only had 350 extra views but my average rating had fallen to 3.54/5.

    So ive been wondering how to work out what the average rating that the last 350 people had given my video. I realise this wouldnt be very accurate over 350 people so ive written a program that checks the webpage with the video on every 1 min and retrieves the number of views and the current average rating. Theres no way i can make sure i get the new rating each time a person watchs the video but the average rating given by the 2 or 3 views i might get in 1 min should be accurate enough to get an idea of any voting patterns.

    Thanks.
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  2. #2
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    Quote Originally Posted by vitaloverdose View Post
    Hi there, ive been posting some videos to the metacafe producer awards program. The idea is that you get paid for your video when you hit 20 000 views if your average rating is above 3/5.Each member of metacafe can rate your video out of 5.

    The other night before i went to sleep i checked one of my vids and it was on 15000 views and had an average rating of 4.2/5.

    When i woke up i had only had 350 extra views but my average rating had fallen to 3.54/5.

    So ive been wondering how to work out what the average rating that the last 350 people had given my video. I realise this wouldnt be very accurate over 350 people so ive written a program that checks the webpage with the video on every 1 min and retrieves the number of views and the current average rating. Theres no way i can make sure i get the new rating each time a person watchs the video but the average rating given by the 2 or 3 views i might get in 1 min should be accurate enough to get an idea of any voting patterns.

    Thanks.
    There is no way the average rating could have fallen to 3.54 from 4.2 with only 350 additional views from 15000. The formula to find the average rating r for the last 350 views is

    \frac{350 \times r + 15000\times 4.2}{15350} = 3.54.

    This says the new average of 3.54 is the weighted average of 4.2 for the first 15000 views and r for the last 350 views. Solving,

    r = \frac{15350\times 3.54 - 15000 \times 4.2}{350} = -24.75,

    which isn't possible. So if you have given us accurate numbers, then there is an error in the calculations for the web page.

    Modify the last formula to calculate the average rating for the last few views.
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  3. #3
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    Thanks for taking the time out to explain how thats worked out.
    Ive checked the figures with a friend who was also keeping track of the ratings for this vid and they agree they are correct. The only thing that might be slightly out is the amount of views i got over night. But that wont be out by much and with an average of -24 i doubt think that adding an extra 1000 views to that formula will produce a result that is acctually possible or very probable and theres no way im out by that much.
    With any luck my program will shed some light on whats going on here.
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