hi,

I'm trying to find a way to calculate confidence level for my ELO rating based on number of games team has played.

In the simplified table below you have a list of games between different teams with result, probability and number of games.

I grouped teams by number of games played.

In this example I wanted to check confidence level for teams with exactly 30 games. Then I tried to find error based on simple calculation of Result - Probability.

Then I calculated standard deviation and looked up confidence level from Z table:

Is this a correct way of finding confidence level based on number of games played? If not could somebody walk me through it step by step please?