Z-score

Z-score is meant to provide an altenative to using score to rank players, since score is not a reliable measure of ability. It is compiled by looking at all of a player's ascensions and assigning 1 point for the first ascension of a role, 1/2 a point for the second ascension, 1/3 for the third, and so on. Z-score encourages playing the complete set of roles rather than repeatedly ascending the same role. For example:

1st wizard	1.00
2nd wizard	0.50
3rd wizard	0.33
4th wizard	0.25
1st priest	1.00
Z-score	3.08

It also encourages ascending multiple variants, since each one has its own Z-score table. The Nethack Scoreboard has an aggregate Z-score table with links to tables for each tracked variant.