X in <CONSTANT> is just the inverse of <CONSTANT> in X. Each is appropriate at different times. 0.0004 is the same as 1 in 2500. I feel like 1 in 2500 is more i

X in <CONSTANT> is just the inverse of <CONSTANT> in X. Each is appropriate at different times. 0.0004 is the same as 1 in 2500. I feel like 1 in 2500 is more intuitive, and that's generally the case for rare events, because it is oriented around answering the question "how rare is this?"