>>31415417I dunno. A simple way would be that the stat would be divided by 10 and subtract from the accuracy of the move.
Example, a Pokemon with 113 Evasion would reduce a 100% accuracy move by 11.3, making it an 88.7% accuracy move.
Of course, stats are never calculated this simply so I'm sure they have some ridiculous formula to apply it if it ever gets used.