Well, without even doing the math, Advantage is of course much better than just +1 to the end result, BUT +1 to the end result can make you win rolls that are otherwise not won.

Thanks to a 20 now being a Critical Success now, this bonus is kind of smaller than in the past.

The most important thing about Advantage is that if you have a spellcaster who can afford to waste a level 2 slot to give you Enhance Ability: Dexterity, you already have advantage and getting an item as well is completely superflous. So then the +1 bonus would be better.



How much does Advantage gain you ? Well:

You roll 2 d20 and take the higher result.

If you roll a single d20, there are 20 possible rolls, and every end result has the same 5% chance.

If you roll two d20 and take the higher roll, then there are 400 possible rolls, and the likeliness of higher rolls is accelerated.

In 39 of these cases, either of the roll was a 20 (19 cases of one being a 20, 19 of the other being a 20, plus the case of both being 20). So your chance for getting a Critical Success raised from 5% to 400/39 = 9.75%, so its almost doubled.

In 37 of these cases, either of the roll was 19 but the other wasnt 20 (again 18 cases of one number being 19, 18 of the other being 19, and one case of both being 19). So thats 400/37 = 9.25%

So the general rule is that (n+n-1)/400 is the chance for the specific roll.

Meaning that every lower roll is 0.5% less likely than the higher.

20 = 9.75%
19 = 9.25%
18 = 8.75%
17 = 8.25%
16 = 7.75%
15 = 7.25%
..
02 = 0.75%
01 = 0.25%

Since 9.75% + 9.25% + 8.75% + 8.25% + 7.75% + 7.25% = 6*8.5% = 51% > 50%, your *average* result is now slightly better than 15 now, instead of being 10.5 before.




Originally Posted by rodeolifant
With no bonuses, you try to pick a DC10 Lock, you need to roll a 10 or higher. On a 20-sided die, that's exactly 50% chance.
Um.

Thats already wrong though.

If you roll a d20, so equal chances for any integer between and including 1 and 20, your chance to roll each possible result is 1/20 = 5%.

If you roll a 1 to 9, you would lose. That 9*5% = 45%.

If you roll a 10 to 20, you win. Thats 11*5% = 55%.

So if you have no bonus or malus whatsoever, its a DC 11 lock that is a 50% chance.