Speaking of calculating odds, does anyone have..., What are the odds of getting a responce? Options

[blakkie]

... a program that can do various d6 odds calculations? Some years back i had one, but that has long since been lost to the big bitstream.

[Sphynx]

Yeah, http://shadowrun.i-sphynx.com has a probabilities calculator on it that gets a few hundred hits a week. It still seems to be highly used. ;)

Sphynx

[gknoy]

I wrote a Perl program that does that last night, actually ...
I can post (or PM) the code for that if you like.

Basically it runs 100,000 (or was it a million?) tests of N dice vs some TN (both are comand line arguments) and prints the average number of successes.

I also have one that prints the average value returned on an open test with N dice. (We had a thread here on that a while back.)

[Lilt]

http://www.pvv.ntnu.no/~bcd/SR/dicerollcalc.html can do some SR-Style probability calculations. I use it for most of my character creation and plain-old pondering calculations. It does variable numbers of dice, TNs, Successes required, and rerolling of failures, but not opposed tests (which would be nice).

[blakkie]

It is an open test that i am interested in. Open tests are by far the toughest to calculate, especially when you start introducing TN modifiers because you have to shift all your open test results before comparing vs. the opposing roll.

Sphynx: Thanks. But it would take some time for me to extract all the data points i need from that. But it's a start. BTW what is that (rerolls) number about? It seems to get higher as the chances drop. Is that how many rerolls you'd need to do to have a 50/50 chance of success?

gknoy: Thanks for the offer but i'm interested more in theoretical valves, and how the curves are shaped on Open Tests.

Lilt: Ok, now that's better. I'll still have to do a bit of data juggling, but allowing a range is what i need.

[Firewall]

Isn't that just basic maths? I mean, doing 1000 tests works but you just need to write a basic tool for calculating the odds.

Statistical analyses are good but I don't trust probabilities, not after walking over to the table and saying 'watch this' before rolling 6 dice - 1,2,3,4,5,6 - Who says magic has not returned yet?

[blakkie]

[RedmondLarry]

[Mathematics]
The probability (a number between 0 and 1) of an Open Test achieving a given Target Number (TN) on DICE number of dice may be computed using the following formula:
1-((1-((1/6)^INT((TN-1)/6))*(6-MOD((TN-1),6))/6)^DICE)

To Try this in Excel, with TN in cell A1, DICE in A2, and the formula in A3, use this formula:

[lordsah]

I've responded to blakkie with the same, but I figured I'd offer to anyone else who'd like it:
About a week ago, I spent an hour coming up with an extensive probability table, which plots TN vs number of dice, and shows the probability of at least 1 {and 2, and 3, etc} successes. It covers up to twenty dice and a TN of 20, and is be easy to extend past that. It also prints nicely in landscape mode.

If you'd like to a copy of the excel file, just let me know at jimgu{at}microsoft.com, and I'll send it your way :)

[lordsah]

[edit]sorry, bad network connectivity

[RedmondLarry]

I calculated an average result for Open Tests. These averages are the point at which 50% of the outcomes are less than that number, and 50% are the given number or greater.

Here's how to read the table:
To get a mean open test result of 4, you need 1 die.
To get a mean open test result of 5, you need 2 dice.

4-1 die
5-2 dice
7-3 dice
8-5 dice
9-6 dice
10-7 dice
11-10 dice
13-17 dice
14-28 dice
15-34 dice
16-43 dice

[blakkie]

lordsah: Forward that Excel file to send_junk_to_me_now#hotmail.com (replace the '#' with '@' in that email address). I'll put it up on my webspace for others to download. If i have time this weekend i might even add the Open Test stuff to it.

OurTeam: The problem with an average number is that it doesn't give enough info about the probability to adjust for TN modifiers, or i suspect even without modifiers. For example from that data can you tell me what the chance of someone making an open test with 6 Stealth dice has vs. an opponent with 3 perception dice? How about if the open test is defaults to 6 Quickness dice (-4 to TN for defaulting to attribute) vs 3 perception dice?

[Zazen]

[Sphynx]

[Lilt]

OK. I've made-up a spreadsheet that calculates the probabilities of getting a particular number as your high-end roll (ranged 2 to 60) when given the number of dice to roll. It also calculates the probability that you will be 'seen' when given the number of perception dice to roll (only works on 1 success so-far, and I've not got it factoring-in perception & camo mods yet).

If you want a copy, just give me your email or tell me where to upload it to.

[edit]Forgot to say: It's in OpenOffice format but I can save it to another format if I need to[/edit]

[Sand]

Using annoying probability math, I did up two sheets. One shows the chance of getting 1+ successes for a given number of dice and TN; the other has average number of successes for a given number of dice and TN. (The second one also serves as a reference for open-ended rolls: just look for the TN closest to 0.5, that's the number you'll get on average.) I was going to attach it to this post...but it seems you can't do that here. :) If anyone's interested I'll happily send it out.

[Lilt]

I got it all working. It seems to be a bit kind to the guy trying to spot the stealthy character, but those may just be my preconceptions. It gives an Int 4 character trying to spot a Stealth 6 character (with camo suit for +4) a 20% chance of 1 success, a 5% chance of 2 successes, and a 1% chance of 3 successes which feels a bit high. I suppose that could be right.

[blakkie]

[BitBasher]

That was me. Open tests are the devil. Open tests are to Shadowrun as Sucking Chest Wounds are to Humans. Not using Open Tests is just like using Soap on a Rope in prison so you dont have to bend over, that is to say it's better for everyone. Open tests, just say no to drugs. Only you can stop Open tests. Open tests cause cancer. Open tests... et tu brutae?

[Lilt]

OK. I fired it off just now in both dummy XL and Open Office formats (XL is 215k, ooffice is 48k, so it should fit in your email).

There is a second page, which has my original calculations, but you can work-out the stuff on there from the main page if you need to.

[edit] Oh yes, and if you're wondering why the probabilities are slightly screwy: It dosen't take into account the rule of the 1. [/edit]

This post has been edited by Lilt: Apr 8 2004, 04:24 PM

[RedmondLarry]

You guys do remember that for an Open Test, using Karma for a reroll let you reroll one of the dice, hoping to get a better number. Right? Tossing in two more points from Karma Pool will let you roll another die, and so on.

SR3.246 Open Tests

[Moon-Hawk]

[Lilt]

Well, my sheet dosen't do karma rerolls anyway but it's a good thing to consider. I too think it would be somewhat more fair if karma bought you a reroll on all but the highest, or if you at-least got a better ratio on the karma expenditire, IE: 2 karma rerolls 3 dice and 3 karma rerolls up-to 6 dice.

[blakkie]

[blakkie]

WOOOYAAA, we are in the :nuyen:.

I just needed to open and F2 each formula to get it to work. Must be an Excel version thing. *shrug* Just trying to force a sheet Recalc didn't work, i actually had to edit (with no changes) each cell individually.

I then tried 6 dice with 3 dice opposing, no TN modifier. That gave me 39.86% chance of the 3 dice opposing getting at least 1 success. That's what i got before using my calcs, so it sounds right. I'll post your file up this afternoon. Tomorrow i'll try incorporating support for penalties on the open test. It should just need an extra if inside that formula to avoid overflowing up past the top of the TN percentage colum.