I've always wondered this but never asked
The catch rate for a Pokémon is based on a formula. The formula does not take stat changes into account.
The formula for determining the capture of the Pokémon is as follows:
CatchValue = ((( 3 Max HP - 2 HP ) (Catch Rate Ball Modifier ) / (3 Max HP) ) Status Modifier
https://www.serebii.net/games/capture.shtml
https://m.bulbapedia.bulbagarden.net/wiki/Catch_rate