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How does chess.com count percentile ?

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giorgiabzianidze

Hello everyone! 
Here are my stats:

I don't understand, why my percentile is 96.3% ? 
There are 29,376,390 players and my rank is 246,881
I guess, it should be counted as
100 - 246,881 * 100 / 29,376,390 
= 99.15 % 
what do you think?

Martin_Stahl
giorgiabzianidze wrote:

Hello everyone! 
Here are my stats:
I don't understand, why my percentile is 96.3% ? 
There are 29,376,390 players and my rank is 246,881
I guess, it should be counted as
100 - 246,881 * 100 / 29,376,390 
= 99.15 % 
what do you think?

That's not how percentiles work.

https://support.chess.com/en/articles/8572866-what-does-percentile-mean

giorgiabzianidze

Could you please let me know where I went wrong?"

Martin_Stahl
giorgiabzianidze wrote:

Could you please let me know where I went wrong?"

Your calculation is a percentage based on the ranking within the total number of players. But that's not what percentile is calculating.

https://en.m.wikipedia.org/wiki/Percentile

giorgiabzianidze

Can you explain it a little better? 
This is what the article says " Percentile is a statistical term that describes the percentage of a group that falls at or below a certain level—in this case, your rating"

Martin_Stahl

While I'm decent at mathematics, I'm no good with statistics. The main takeaway is that there are lots of members with the same ratings and they are grouped together in the percentile groupings so it's not a simple percentage calculation.

giorgiabzianidze

I am decent with statistics.
Grouping members with the same rating doesn't make sense, that should not be the case.

Martin_Stahl
giorgiabzianidze wrote:

I am decent with statistics.
Grouping members with the same rating doesn't make sense, that should not be the case.

Percentile is a statistics term with a specific meaning and definition. Someone with a fuller understanding of that probably could explain it best.

This is Google's number 1 recommended site for that

https://www.simplilearn.com/tutorials/data-analytics-tutorial/percentile-in-statistics

Martin_Stahl

So this

  • In statistics, a percentile is a term that describes how a score compares to other scores from the same set. While there is no universal definition of percentile, it is commonly expressed as the percentage of values in a set of data scores that fall below a given value.

which means that everyone that has the same rating as you is in your cohort and essentially don't count towards the calculation (only those below do)

giorgiabzianidze

Users with the same rating as me are not that much. 
I am talking about a 3% difference in my case. 
Percentile should be 99.15% and chess.com shows 96.3%. 

Martin_Stahl
giorgiabzianidze wrote:

Users with the same rating as me are not that much. 
I am talking about a 3% difference in my case. 
Percentile should be 99.15% and chess.com shows 96.3%. 

There are around 350,000 members with 1700 or higher ratings which is 1.2% of players higher rated than you. There are another 150,000+ members between 1600 and 1700. Using that basic calculation, which isn't appropriate for percentile, would put closer to 1.7% likely above the rating in the first post and you closer to the 98.3 percentile

I won't say for certain the site's calculation is 100% accurate, just that your calculation of percentage. Is not percentile and not what is being calculated.

Khnemu_Nehep
giorgiabzianidze wrote:

I am decent with statistics.
Grouping members with the same rating doesn't make sense, that should not be the case.

Yes it does. You're not better than people with the same rating as you.

Giganti18
Khnemu_Nehep wrote:
giorgiabzianidze wrote:

I am decent with statistics.
Grouping members with the same rating doesn't make sense, that should not be the case.

Yes it does. You're not better than people with the same rating as you.

"Users with the same rating as me are not that much. 
I am talking about a 3% difference in my case. 
Percentile should be 99.15% and chess.com shows 96.3%. "

bblatter

Giorgiabzianidze is correct. I suspect the reason why a rank of 246,881 isn't in the 99th percentile is because only players active within the last 90 days are counted. So while it says there are 29 million players, it doesn't clarify whether this is total players or total active players. If there are 29 million players and let's say 6.7 million of them were active in the last 90 days, then the 96th percentile stat makes sense.

giorgiabzianidze

bblatter yes, I agree with you, I suspected that too.

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