The original D&D edition, AD&D, and Basic all had the Prime Requisite mechanic, in which all classes have one main ability score that affects the amount of XP they get. It’s a modifier that gets applied to all XP a character gets before they are added to the character’s XP total. In B/X (where I will be taking all further numbers from) the modifier ranges from -20% for a score of 5 or lower, to +10% for a 16 or higher. Which sounds quite significant when you put it like that, but actually makes a much smaller difference than you might expect, because of the way XP requirements to reaching the next level increase.
The way it’s supposed to be done is that the GM announces the amount of XP every player gets, and the players have to remember to apply their relevant modifier to that number before adding it to their total. (I don’t exactly have high trust in this.) Since the players might encounter various magical effects that increase or decrease their ability scores, and potentially change their XP modifier, I can see why this approach was chosen, instead of having five different columns for XP needed by each class based on the prime requisite score. But to make the comparison easier, I did just that with the XP requirements for fighters. Because adding and subtracting percentages changes the outcome based on the order of operations, a -20% to all XP gained translates to the character requiring 125% the amount of XP to reach any given level. And a +10% bonus to all gained XP means a requirement of 91% the XP to reach the same level.
How does this translate to characters advancing through levels faster or slower? Of course, a character with a very high prime requisite score will reach Nth level before a character with a very low score. But how big is that advantage in the long run?
- At 10,000 XP, a Fighter with a -20% penalty will have reached 4th level, and a Fighter with a +10% bonus will still be 4th level.
- At 50,000 XP, a Fighter with a -20% penalty will have reached 5th level, and a Fighter with a +10% bonus will still be 5th level.
- At 100,000 XP, a Fighter with a -20% penalty will have reached 7th level, and a Fighter with a +10% bonus will still be 7th level.
- At 500,000 XP, a Fighter with a -20% penalty will have reached 10th level, and a Fighter with a +10% bonus will be ahead at 11th level.
It is only at the point where the GM has awarded all characters 72,000 XP and a Fighter with no modifier has reached 13th level that there’s an actual gap to Fighters with a -20% penalty, who are still at 11th level. And that’s for the extreme cases where a player with a Strength of 5 or lower decides to play a Fighter anyway for shits and giggles. Such characters being played up to 11th level probably isn’t going to happen in a terribly high number of campaigns. If we narrow the scope to only penalties of -10% and bonuses of +10%, the effect becomes even significantly smaller.
It’s even more marginal in AD&D, where characters can’t have any penalties and it’s only the default XP or +10%.
This does not seem like something that is worth accounting for. Having players with high or low prime requisites remember to apply the modifier every time they get XP does not seem worth the near undetectable difference in results to me. If you have two characters with the same class start at the same point, then yes, sometimes one player might announce that he reached a new level before the other player. But if either of those two characters misses out on a single session, or gets disabled and gains no XP in one session,, that pattern will already be completely out of whack anyway.
In my opinion, prime requisites make too little impact to be worth bothering with. I’ve come around on my earlier opinion that all classes should just use the Fighter XP requirements because the level difference between a Thief and a Wizard with the same XP really is quite substantial. (A wizard needs +100% the amount of XP that a Thief needs!) But prime requisites is something I threw out right when I started running B/X games, and that under closer statistical observation, I still see no reason to bring back.