How to calculate scores?

Question

Hi, This question is more related to logic than any programming language. If the question is not apt for the forum please do let me know and I will delete this.

I have to write a logic to calculate scores for blogs for a Blog Award website. A blog may be nominated for multiple award categories and is peer-reviewed or rated by a Jury on a -1 to 5 scale (-1 to indicate a blog they utterly dislike). Now, a blog can be rated by one or more Jurors. One criterion while calculating final score for a blog is that if a blog is rated positively by more people it should get more weightage (and vice-versa). Similarly a blog rated -1 even by one Juror should have its score affected (-1 is sort of a Veto here). Lastly, I also want to have an additional score based on the Technorati rank of the blog (so that the final score is based on a mix of Juror rating + Technorati ranking).

Example: A blog is rated in category A by total 6 Jurors. 2 rate it at 3, 3 rate it at 2 and 1 rate it at 4. (I used to calculate the score as (2*3 + 3*2 + 1*4)/6 = 16/6 = 2.67 to get weighted average but I am not satisfied with this, primarily because it doesn't work well when a Juror rating is -1. Moreover, I need to add the Technorati ranking ranking criteria too) .

Could you help me decide the best way to calculate the final scores (keeping the rating method same as above as that cannot be changed now)?

Answer 1

you could internally work with scores from 0 to 6. Just do a shift by one, calculate the score and shift back. I guess the -1 has some disrupting effekt on your calculation.

Answer 2

If you want to weight the effect of a -1 rating more strongly, use the same average score calculation but substitute -10 whenever you see -1. You can choose a value other than -10 if you don't want a negative rating to weight as strongly.

Answer 3

Calculating a score based on votes will be pretty easy. Adding the technorati rank will be the tricky part.

I made a quick script that calculates some scores based on this algorithm

score = ( vote_sum - ( vetos * veto_weight ) ) / number_of_votes

you can change the url paramters to get different values

There are a lot of ties, so maybe you could use technorati blog rank as a tie breaker

Answer 4

You might look at using the lower bound of the Wilson score interval for your ratings.

See http://www.evanmiller.org/how-not-to-sort-by-average-rating.html for more details. Although, there, it is used for the simpler Bernoulli case.

The gist is if you have a lot of ratings you have a higher degree of confidence in your scoring. You can then combine the scores from your local ratings and the Technorati ratings, by weighting the scores by the number of voters locally and on Technorati.

As for wanting a single -1 vote to have high impact, just remap it to a large negative value proportional to your desired impact before feeding it into your scoring formula.