Dimsas's blog

On what criteria is the rating of a problem calculated?
By Dimsas, history, 20 months ago, In English

The difficulty level of some problems seems to be well below or above what the rating indicates, so I was curious as to what criteria problem ratings are calculated upon.

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20 months ago, hide # |
 
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I think it has something to do with the amount of submissions the problem records within a contest,you'd notice a lot of div3 D's and E's are rated 1400-1500 but are considerably easier than a div2C or a div1A of the same rating.

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20 months ago, hide # |
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i think it has to do with the amount and the rating of people solved it during the contest, also div2 problems that get a rating of 1400 — 1500, sometimes are harder than div3 problems getting rating of 1500 — 1700

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20 months ago, hide # |
 
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A problem gets a rating of X in a contest if 50% of participants of rating X solved it during the contest

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    20 months ago, hide # ^ |
     
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    Ah I see Do you have a source for this??

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      20 months ago, hide # ^ |
       
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      As far as i know Codeforces uses the ELO rating system

      To calculate the performance of a problem we need to see how many participants of which rating it defeated during a contest(participants that failed to solve it), then you use the ELO performance formula to calculate its rating.

      Now we can arrive to a Winning probability table based on ELO difference where you can see that if the rating difference gets close to 0, the winning probability gets close to 50%, thus if a problem defeated 50% of participants of rating X the problem has a rating of X.

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