D&D 5E Advantage / Disadvantage in 5e

Coredump · Mar 1, 2015

Gecko85 said:
Yes, but if you need a 15 on the roll instead of 16, you're better off with advantage (+4.2).

Which is meaningless, since making the comparison after the first die is cast is nonsensical....

Eejit · Mar 1, 2015

Coredump said:
The issue is how 'valuable' is getting advantage. So if you needed a 16 to hit, would you rather have advantage on the roll, or a +4 on the roll?
As it turns out, you are better off with the +4. (Advantage would be the equivalent of a +3.75 on the roll) The benefit from advantage is never better than a +5 on the roll, and can be worse than a +1.

The numbers below are accurate.

Sure, but isn't that kind of meaningless? You never get to choose between Advantage and a flat bonus IIRC. So you don't really have anything in 5E to compare the value of advantage to.

Henry · Mar 1, 2015

fjw70 said:
An AD&D character could get a +14 or 15 to hit. A 10th level fighter's THACO was effectively a +9 and add in magic weapons, and strength and specialization bonuses would get you into that range.

Hence the "rarely".

by the time we were 8rh or 9th level, a year's time had passed, and someone was ready to run a new campaign, or the group shifted meaning it was time to change to a new campaign. I have a book of my old characters from before the year 2000, and inly one of them is 10th level, i think, with a majority of them between levels 4 and 7. Playing by the old XP system, it took us about 5 to 6 months of weekly play to hit level 7 (except for clerics and rogues), and then another 3 or 4 to hit level 9, and about a month per level after that.

It's kind of funny thinking about using XP to level now -- I probably havent done that in 7 or 8 years, now.

Nebulous · Mar 1, 2015

Henry said:
It's kind of funny thinking about using XP to level now -- I probably havent done that in 7 or 8 years, now.

Me neither, I dispensed of that system many, many years ago and greatly enjoy the game better without it.

GMMichael · Mar 1, 2015

@Mark CMG, good quote. The online basic rules don't go into that depth, so I'm glad you found a better source for me.

Coredump said:
The issue is how 'valuable' is getting advantage. So if you needed a 16 to hit, would you rather have advantage on the roll, or a +4 on the roll?
As it turns out, you are better off with the +4. (Advantage would be the equivalent of a +3.75 on the roll) The benefit from advantage is never better than a +5 on the roll, and can be worse than a +1.

The issue I raised was (explicit or not): how valuable is ADV/DIS on average? I've seen only one refutation of the question I was asking, from @fjw70, who may have provided the key to the puzzle. (Yes, puzzles have keys.)

@Coredump: I'm going to assume your argument is invalid based on this: if I roll a 1 and a 20, my advantage benefit is +19 or +0, an average of +9.5, which is better than +5. Did you mean the average benefit is never greater than +5?

fjw70 made me ask myself: does advantage's advantage depend on sequence of rolls? Can advantage be said to grant a benefit if both rolls are made at the same time? My method assumed that the rolls did not depend on order, and that advantage was always increasing the result of the lower roll to the higher roll. Question 1: why is this incorrect?

Now if I say order is important, that advantage always follows a normal roll, this means that the second roll is worthless if it is equal to or lower than the first. In this case, advantage has granted no advantage at all. This will significantly lower the average bonus, but it also seems to state that almost half of the time (get this): advantage negates itself. Actually, over half the time, since equal results on the dice are effectively no advantage, too.

The average benefit from this method is: 3.325.

Question(s) 2:
So is @Gecko85 right (3.325), and advantage usually isn't advantage at all?
Or am I right (6.65), and advantage is always advantageous?
What's another possibility?

Mark CMG · Mar 1, 2015

DMMike said:
Mark CMG good quote.

De nada, Mazmorra Maestro Miguel.

DMMike said:
The online basic rules don't go into that depth, so I'm glad you found a better source for me.

That's where this came from (though I had it from my v0.1 first and now had to check if v0.2 has the same text).

http://dnd.wizards.com/articles/features/basicrules

http://media.wizards.com/2014/downloads/dnd/PlayerDnDBasicRules_v0.2_PrintFriendly.pdf

Gecko85 · Mar 1, 2015

Coredump said:
Which is meaningless, since making the comparison after the first die is cast is nonsensical....

I'm not sure what you're trying to say. You originally said:

So if you needed a 16 to hit, would you rather have advantage on the roll, or a +4 on the roll?
As it turns out, you are better off with the +4

I countered with:

Yes, but if you need a 15 on the roll instead of a 16, you're better off with advantage (+4.2)

So, not sure what you're trying to say about comparisons and first die...

The odds of getting at least a specific target when throwing two dice are the odds - there is no first die and second die. The odds are for two dice.

The benefit of advantage, on average, is equivalent to just over +3. Sometimes more, sometimes less. Never more than +5, sometimes just under +1 (+.95). This makes sense. Remember that the target roll is what you need to roll after bonuses. Let's say you're trying to attack a very tough, nearly impossible to hit foe...or attempting a very hard acrobatic move. Let's say you have +5 on your roll (either a to-hit bonus or acrobatics proficiency). The target AC or DC is 25...so, you need a natural 20 to succeed. Without advantage, you have a 5% chance of success. With advantage, you have just under 10% chance, the equivalent of +0.95. Your chance of success with advantage is still very low, as it should be, but it's nearly double the odds of no advantage.

Gecko85 · Mar 1, 2015

Sorry, duplicate.

Gecko85 · Mar 1, 2015

DMMike said:
if I roll a 1 and a 20, my advantage benefit is +19 or +0, an average of +9.5, which is better than +5. Did you mean the average benefit is never greater than +5?

Sorry, but your math/assumptions are incorrect. There is never a "+19" benefit for advantage. Advantage is *always* the probability of hitting a specific target or higher when rolling two dice. I've already posted those probabilities. The probability is a percentage, but we can give it as an *equivalent* bonus as if we had just rolled one die because we know the odds for rolling any single number on a d20 is 5%. So, there's never more than a 25% better chance (or, the equivalent of +5) when using advantage.

fjw70 made me ask myself: does advantage's advantage depend on sequence of rolls? Can advantage be said to grant a benefit if both rolls are made at the same time? My method assumed that the rolls did not depend on order, and that advantage was always increasing the result of the lower roll to the higher roll. Question 1: why is this incorrect?

Now if I say order is important, that advantage always follows a normal roll, this means that the second roll is worthless if it is equal to or lower than the first. In this case, advantage has granted no advantage at all. This will significantly lower the average bonus, but it also seems to state that almost half of the time (get this): advantage negates itself. Actually, over half the time, since equal results on the dice are effectively no advantage, too.

Again, the assumptions are wrong. When using advantage, you roll two dice. The probability of rolling a target number or higher are based on rolling two dice, not rolling 1 die then another. There is no first die, second die. There are only both dice. Statistically, per the laws of probability, order does not matter.

Question(s) 2:
So is @Gecko85 right (3.325), and advantage usually isn't advantage at all?
Or am I right (6.65), and advantage is always advantageous?
What's another possibility?

It's not a matter of me being right. The math is the math. Probability is probability. It's calculable. The average equivalent benefit of advantage is +3.325 (or, about 16%). The actual benefit, though, changes depending on what your target number is. And, I'd say it's very advantageous. It's as high as 25% (for a target of 11). So, if you need to roll an 11 or higher, you have the equivalent of +5 on your roll. That's huge. Even the lowest percentage advantage (for rolling a natural 20) is double with advantage than without, even if it's still relatively small. So, again, the average equivalent advantage is +3.325, which is very advantageous. It's never 6.65, because that's not how probability works.