I haven't tested this, but try something like
IF INDEX([state]) < COUNTD([state)]/3 THEN "P1"
ELSEIF INDEX([state]) > COUNTD([state])*2/3 THEN "P3"
Hope this helps!
Woops, seems like I not only used the wrong function, but also misread your initial question. Sorry about that.
Please disregard my previous post.
What field did you use to calculate the numbers next to your States?
It is Sum(Number of Records)