Percentile D&D Ability Score Generation

James over at Grognardia put up a post about Ability Score Handicapping and talking about the ability score generation methods of games other than D&D. One of them, taken from FGUs Space Opera has a percentile based table that generates a score between 1-19 for each stat. The interesting bit (for me) is that different stats use different percentile ranges to cross-reference with the attribute scores – so a roll of 90 will net you a 16 Strength, but only a 15 Dexterity or a 14 Intuition. He finished by musing if this and the other tables presented (which I confess I only skimmed over as my brain was already firing..) could be used as the basis for some alternative ability score generation methods.

Well, here’s my take on it using a d100 against the traditional 3-18 range to keep things within the parameters of the other methods:

Ability Score	D100 Roll	Probability
3	01-02	2
4	03-04	2
5	05-06	2
6	07-08	2
7	09-13	5
8	14-18	5
9	19-23	5
10	24-28	5
11	29-38	10
12	39-53	15
13	54-68	15
14	69-78	10
15	79-88	10
16	89-93	5
17	94-98	5
18	99-00	2

So.. the average character has:

• A 2% chance of having an 18 in any given score – where I see 18 as being the maximum normal (demi)human score.
• A 47% chance of having at least +1 in a given score.
• An 82% chance of scores between 9 and 18 – so average or better

I guess if you want to fiddle the odds a bit you could bump the probability of getting a 14 up to 15% and drop those of getting a 12 to 10%. That gives you a 52% chance of getting a +1 or more.

Not enough? Also drop the chance of getting an 11 to 5% and bump the chance of a 15 up to 15%. That way you’ve got a 45% chance of getting a +1, 10% of a +2 and 2% of a +3.

The upshot is that you’d end up with characters that are weighted to towards the positive end of the spectrum but 18 remains an outlier.

Also, if my thinking is correct, by keeping the distribution as per the table, you’ll end up with a bunch of stats at 11 & 12 which – if a character is lucky enough – could be increased with magic and put the character into bonus territory. 

Finally – I’ve only sketched out a ‘generic’ table that could be used for all 6 Abilities. However, I think the premise may work well if it’s extrapolated – as with Space Opera – to give differing distributions to different stats, depending on your wants and needs as a DM.