Just how good is rolling twice?

[phaed]

I proved the 13.825 number abstractly, you didn't need to run a million experiments.

I was actually responding to Aloïsius's quote and somehow missed/skipped your post (boy do I feel dumb!)

If I had known the math for it I would have used that, but from my perspective spending 5 minutes of coding time and a second of cpu time was easier than finding the appropriate math for it

I also agree that taking a reroll is going to be better pretty much across the board with 4e's goal of 50/50 success on checks.

 

[Pierson_Lowgal]

site:gleemax.com danger sense improved initiative - Google Search

Several comparisons of improved initiative and danger sense, which would seem to be right to your point.

My understanding is that rolling twice is superior when in order to succeed you need a die roll in the middle, and a bonus is superior when you need a very low or very high die roll to succeed.

 

[HighTemplar]

As long as everyone understands that rolling twice is very different than rolling re-rolling and keeping the second result.

Re-rolling in this case yields different results depenging on the "target number" (sorry about the shadowrun vocab) that you need on your D20.

Rolls...................................Expected value [average bonus on D20]
simple roll : ..........................................10.5
Better of 2 rolls : ..................................13.825 [+2.325]
 
Re-rolling against secret difficulty: ...........13       [+2.5]
([I]The above implies you only re-roll when you get 10 or less[/I])

Re-Rolling VS target number
(Suppose the roll is DC 30, and you have +18, your target number is [DC-Skill total mod = 12])

Target number........[Equivalent bonus on the D20] asolute chance of success
20............................................+19/20 [+0.95]  9.75%
19............................................+36/20 [+1.80] 19%
18............................................+51/20 [+2.55] 27.75% 
17............................................+64/20 [+3.20] 36%
16............................................+75/20 [+3.75] 43.75%
15............................................+84/20 [+4.20] 51%
14............................................+91/20 [+4.55] 57.75%
13............................................+96/20 [+4.80] 64%
12............................................+99/20 [+4.95] 69.75%
11............................................+100/20 [+5]    75%
10............................................+99/20 [+4.95] 79.75%
9..............................................+96/20 [+4.80] 84%
8..............................................+91/20 [+4.55] 87.75%
7..............................................+84/20 [+4.20] 91%
6..............................................+75/20 [+3.75] 93.75%
5..............................................+64/20 [+3.20] 96%
4..............................................+51/20 [+2.55] 97.75%
3..............................................+36/20 [+1.80] 99%
2..............................................+19/20 [+0.95] 99.75%

 

[kouk]

Hmm. I'm bad at math, but would Sure Strike (Ranger At-Will with +2 bonus to attack roll, single attack) be better than Twin Strike (two attacks) if you have a reroll power such as Elven Accuracy?

 

[Cadfan]

kouk- Not necessarily. First, you have the practical problem that you probably don't want to use your per encounter Elven Accuracy on an at will instead of a bigger power like a per encounter or per day attack. Second, Twin Strike has the potential to hit with both attacks, giving it a higher damage. I could do the numbers, but I think the first problem is big enough that I don't think its worth relying upon the Sure Strike / Elven Accuracy combination.

 

[-Avalon-]

And, what are the rough chances of an Elf hitting a Halfling? and what modifiers would make one or the other more or less successful?