Sneak attacks vs Concealment, balance or common sense ?

[Chiaroscuro23]

Actualy it not a cumulative shot.

It is a 20% miss chance and then another 20% miss chance since it is a separate roll. It is not 20% of 20% regardless of how "it seems to be".

And to get the likelihood of two independent events both happening, you multiply the chance of each, right? So yeah, the chance of missing is reduced by blind fight. Now, whether that negates the rules about concealment is separate, of course.

-C.

 

[starwed]

Why should a rogue who can't see well fight better than someone else who also cannot see well?

Um, because they're rogues? ^_^ I think the point is that rogues are specially trained and/or naturally adept at being sneaky bastards, and part of that is (traditionally) sneaking about in the dark and stabbing people.

The fact that your average rogue can't do this in D&D is what seems odd to some people. Sure it makes mechanical sense, but it doesn't jibe with the flavor some people are after.

Personally I'd want even 1st level rogues to have an advantage in a dark alley, so even FtDM's rule is a bit too restrictive for me. If you want to preserve some penalty for the sneak attack, maybe rolling an additional miss chance for it would work, or simply subtracting one from each die roll.

 

[Plane Sailing]

Actualy it not a cumulative shot.

It is a 20% miss chance and then another 20% miss chance since it is a separate roll. It is not 20% of 20% regardless of how "it seems to be".

I think you are mistaken.

In order for you to actually miss, you have to roll 20% on the first check and 20% on the recheck. 1 in 5 is the basic failure; if you have blindfighting though then only 1 in 5 of those failures is actually a failure - i.e. 1 in 25 chance of a failure to hit someone who has partial concealment if you have blindfighting.

The chance of failing both is thus 4%

 

[irdeggman]

I think you are mistaken.

In order for you to actually miss, you have to roll 20% on the first check and 20% on the recheck. 1 in 5 is the basic failure; if you have blindfighting though then only 1 in 5 of those failures is actually a failure - i.e. 1 in 25 chance of a failure to hit someone who has partial concealment if you have blindfighting.

The chance of failing both is thus 4%

Probability does not work that way though.

Each and every roll is a new one for determining actual probability.

If you had a percentage of a number like for sales tax or something like that you would be correct, but not for probability.

 

[Infiniti2000]

Probability does not work that way though.

Each and every roll is a new one for determining actual probability.

It works exactly that way for independent events.

http://mathworld.wolfram.com/IndependentStatistics.html

You might be thinking it's conditional, but it's not.

 

[nittanytbone]

This explains why fantasy cities are spooky with poor illumination -- bright lighting actually encourages crime!

 

[Infiniti2000]

This explains why fantasy cities are spooky with poor illumination -- bright lighting actually encourages crime!

Well, the key for the rogues is to be within concealment (at the edge of it actually) and target victims not in concealment. So, to reduce the chances of an one-round kill against you, you should stay in the shadows.

 

[Quartz]

It works exactly that way for independent events.

http://mathworld.wolfram.com/IndependentStatistics.html

You might be thinking it's conditional, but it's not.

You're both wrong. The calculation depends how you throw the dice.

If you throw both dice at the same time, what you need to calculate is the chance of at least one attack hitting. To do this, you calculate the chance of both missing, and substract it from 1. So the probablility is 1-(0.2x0.2) = 1-0.04 = 96%

If you only throw the second die after the first is shown to miss, you apply Bayes' Theorem which gives P_Miss(Hit)=P(Hit and Miss)/P(Miss) and multiply it by the probability of missing in the first place. Then subtract from 1 to get the same result as above.

 

[Infiniti2000]

You're both wrong. The calculation depends how you throw the dice.

No, it doesn't. Your second method incorrectly assumes a conditional probability, and it's not.

 

[Christian]

I2K and PlaneSailing are correct. Here's another way to calculate it if you're doubtful ... Suppose you get 100 hits against an opponent with concealment. That's a 20% miss chance, rolled twice because you have Blindfighting. Well, 80 times out of the 100 (on average), you roll higher than 20%, and confirm your hit. The other 20 times, you still get to roll the miss chance again; of those 20 rolls, 20% (4, again on average) show you miss again, while the other 80% (16) of the time you actually hit successfully. So, in 100 hits on the d20, you end up with 96 (80+16) hits after the miss chance rolls, and only miss because of concealment 4 times, or 4% of the time.