P(n) = 1 - (1 - P(1))^n
I understood it differently. It rolls once, and depending on that roll it will shake the corresponding number of times.As I understand it, the normal catch rate rolls 4 times, puts them through some ugly formula, and compares the result to the target number. All 4 rolls have to succeed in order to catch it (the ball will shake once for each success). A critical catch only rolls once, which is why it only shakes once, but that one roll still has to succeed. It's still much more likely, but it's not guaranteed by any means.