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Roj 
Special Collaborator 
Honorary Collaborator Joined: July 02 2008 Location: Manchester, UK Status: Offline Points: 3126 |
 Topic: Strange Change in Album RatingPosted: September 08 2008 at 09:23 |
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I hope I am posting this question in the correct section. Here goes, anyway.
Today I placed a review of Chronometree by Glass Hammer, which before my review was averaging 2.92, based on 27 reviews. I gave the album 4 stars in my review, yet it's average has now gone DOWN to 2.89 following my review! Any ideas why this has happened?
Thanks, Roj.
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chopper
Special Collaborator
Honorary Collaborator Joined: July 13 2005 Location: Essex, UK Status: Offline Points: 20033 |
Posted: September 08 2008 at 10:16 |
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It may be something to do with collab reviews getting a higher rating, but you really need MikeEnRegalia to explain the algorithm.
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MikeEnRegalia
Special Collaborator
Honorary Collaborator Joined: April 22 2005 Location: Sweden Status: Offline Points: 21616 |
Posted: September 08 2008 at 10:54 |
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^ I used to know how it works ... but M@x made some significant chances since then.
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Padraic
Special Collaborator
Honorary Collaborator Joined: February 16 2006 Location: Pennsylvania Status: Offline Points: 31169 |
Posted: September 08 2008 at 11:00 |
That should only mean that the overall rating wouldn't increase as much as it would if a collab gave it four stars....but there's no explanation for the rating decreasing in value. |
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chopper
Special Collaborator
Honorary Collaborator Joined: July 13 2005 Location: Essex, UK Status: Offline Points: 20033 |
Posted: September 08 2008 at 11:16 |
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It would if the algorithm caused Roj's rating to be less than the 2.92 average. I may be barking up the wrong tree anyway, looks like we need M@x to explain.
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Roj
Special Collaborator
Honorary Collaborator Joined: July 02 2008 Location: Manchester, UK Status: Offline Points: 3126 |
Posted: September 08 2008 at 11:23 |
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Easy Livin
Special Collaborator
Honorary Collaborator / Retired Admin Joined: February 21 2004 Location: Scotland Status: Offline Points: 15585 |
Posted: September 08 2008 at 11:35 |
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I believe the rating is affect not only by reviews of the album in question, but by reviews of other albums which contribute to the overall weighting.
Bear in mind too that someone else may have submitted a rating only around the same time, and that the calculations are cached, i.e. they do not always update instantly.
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Padraic
Special Collaborator
Honorary Collaborator Joined: February 16 2006 Location: Pennsylvania Status: Offline Points: 31169 |
Posted: September 08 2008 at 11:41 |
If indeed this is the case I would claim that the algorithm is seriously flawed. |
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Roj
Special Collaborator
Honorary Collaborator Joined: July 02 2008 Location: Manchester, UK Status: Offline Points: 3126 |
Posted: September 08 2008 at 11:44 |
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Natural Science ^ I agree entirely
It would be nice if a positive review had a positive ( albeit minor I appreciate ) effect on the rating. God only knows what would have happened if I'd rated it 1 star, as opposed to 4 stars!
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MikeEnRegalia
Special Collaborator
Honorary Collaborator Joined: April 22 2005 Location: Sweden Status: Offline Points: 21616 |
Posted: September 08 2008 at 11:58 |
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Maybe I know what's happening. If I remember correctly, the current algorithm combines the average of all the albums with the average which results from all the ratings for the album:
AVG = (R*N+r*n)/(N+n) R = Average of all the ratings in the database (currently about 2.9 EDIT: what was the number again? Maybe M@x could clarify) N = Average number of ratings per album r = average rating of the album in question (arithmetical mean) n = number of ratings for the album in question Now, if currently r is well above 4, an additional 4 star rating might actually decrease the result.    Edited by MikeEnRegalia - September 08 2008 at 12:01 |
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Padraic
Special Collaborator
Honorary Collaborator Joined: February 16 2006 Location: Pennsylvania Status: Offline Points: 31169 |
Posted: September 08 2008 at 12:01 |
But in this case r appears to be below 3! Your statement is just common sense - if the album average is well above 4, a rating of exactly 4 will lower it. Edited by NaturalScience - September 08 2008 at 12:02 |
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MikeEnRegalia
Special Collaborator
Honorary Collaborator Joined: April 22 2005 Location: Sweden Status: Offline Points: 21616 |
Posted: September 08 2008 at 12:02 |
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^ I edited the post ... in retrospect I think the average is at 2.9, not 3.9. It would be useful if that value was posted somewhere on the website ...
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Roj
Special Collaborator
Honorary Collaborator Joined: July 02 2008 Location: Manchester, UK Status: Offline Points: 3126 |
Posted: September 08 2008 at 12:19 |
 Sorry, maths never was my strong point.
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M@X
Forum & Site Admin Group
Co-founder, Admin & Webmaster Joined: January 29 2004 Location: Canada Status: Offline Points: 4076 |
Posted: September 19 2008 at 01:55 |
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Guys,
Sorry for the delay , i was out for 2 weeks. The problem (i hope not too global) is related to a problem in older calculation of the avg. rating of the specified album in the past, data corruption. So the last review/rating posted made it recalculate correctly the new avg. rating and now giving the correct value. I will investigate more about this.. thanks for reporting Max |
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Prog On !
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Strange Change in Album Rating
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chopper wrote: