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The arithmetic mean or average is easy to implement since it's often integrated as a function in most programming languages.

However, it's not really appropriate for ratings as several 5 out of 10s would "drag" down the average whereas a single rating of, say, 8 would give a higher average.

What calculation is usually done instead on sites that let you rate pictures or people? I'm supposing that weight is given to a higher number of ratings.

PeeHaa
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James P.
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2 Answers2

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I think your best bet is to ignore the outliers - ie discard the top 10% and the bottom 10% and then calculate the average

Alternatively, maybe re-think exactly what you want to do, maybe have some way of assigning weights to the voters

Alftheo
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  • The first approach sounds like cutting out the extremes in a bell curve. I'm not quite sure how this could be done in SQL. Maybe get the number of ratings, do a SELECT ... LIMIT for the 10% then do a SELECT ... NOT IN ... . – James P. Jun 15 '11 at 13:45
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I've heard online that median is a commonly used alternative to mean, usually in skewed settings. In symetrical data sets, the mean, median and mode are the same.

ebp011
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