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107 posts tagged with probability.

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## Too Many Strata To Sample

I have multiple independent variables that I want to stratify my sampling across, but the result would be way more strata than I can sample. Is there a way to stratify across different character states for each independent variable without creating strata for the interactions of each? Example inside. [more inside]

## Can you figure out the probability of a specific outcome?

I work in a field where we think about possibly dangerous people. If Mr. X is a poor driver and has a 5% chance of running a red light in the next month, can you know the probability of him running a red light at a specific intersection? Can you know a range of probabilities for that specific intersection? What if it's the intersection that he drives through most often? I think this likely has an easy answer but none of us can clearly explain it so we keep talking about it.

## Statistical framing of the engineering and extremism article

Reading this article on the blue got me thinking about conditional probabilities, prediction and causality. I came up with an analytical framing of what I think the article is saying and would be grateful if stats/social science Mefites could tell me if it seems accurate or else set me right. [more inside]

## How often to roll 2d6 a special way to guarantee an outcome once?

There is an 8/36 chance that a

*very particular outcome*can be generated by rolling 2d6*in a particular way*(both described after the jump). How many times do I need to roll to be certain that this outcome occurs (ie, I can stop rolling)? How about 90 per cent certain? 80 per cent? [more inside]## Probability and choice

I was reading a book on probability and decision making several years ago and it mentioned a rule of sorts that could be used when making a selection from a sample that would help you make an efficient decision that was likely to gave a good outcome. [more inside]

## How to Math

I'm a computer science major in college. I'm not a freakin' genius, but I do well-- get A's in my classes, good with abstraction (e.g. pointers), etc. However, I seem to have missed... my entire high school pre-Calculus math curriculum? I don't know. [more inside]

## Calculating the probability of a scenario that might happen by chance

I have to validate some input for a database, and I want to present the user with a mathematically accurate estimate of the percentage of data that they entered which may be invalid. The problem is that valid data looks like invalid data 10% of the time. [more inside]

## Probability distributions and their practical applications

I am looking for a resource that lists probability distributions and their common real-world applications. For example, I'd expect to see: Lognormal - daily returns in the stock market. Poisson - failure rates for mechanical equipment, ... [more inside]

## Predictive analytics basics for programmers?

I'm looking for resources that discuss the basics of data mining and building predictive models. [more inside]

## Best or most appropriate Statistic method to Use.

I have a statistics and/or probability question and the last time I took a statistics class Vanilla Ice and Andrew "Dice Clay" were multi-millionaires.
I am not looking for a problem to be solved, I am asking what statistical technique should I use to determine if a time series of data is due to randomness or not. [more inside]

## Statistics are hard.

How do you calculate the probability of something when it's not as simple as "do it a bunch of times"? Specifics inside. [more inside]

## Fruit salad for statisticians

What formula do I need to determine the probability that a set of size N contains two elements, each appearing with a specific frequency? [more inside]

## Travel 5 weeks before wife’s due date? Chances of missing the birth?

I'm thinking about being a away for a week, around 4-5 weeks before my wife's due date. I'm looking hard statistics (chances of missing the birth) and soft advice (what would you do) to help with this decision. [more inside]

## Math Problem

Please help with this probability related math problem. [more inside]

## Math / probability question re: HIV

I'm trying to calculate the probability of contracting HIV for the husband of an infected woman.
Given a risk of 10-50 conversions per 10,000 exposures. And assuming an average frequency of sexual acts of 2-3 X per week. That's 100-150 sexual acts /year. That should give about a 10%-15% yearly risk of contracting HIV, right?

## Has a major lottery ever produced a result that doesn't look random?

Every outcome in a fair lottery is equally probable, yet some results display obvious patterns and feel less likely to the statistically uninformed. Nobody would blink if a six-number lotto draw came up with (3,12,27,31,40,44), but a result of (1,2,3,4,5,6) would probably make the news. Has this ever happened in a major lottery? If yes, what was the public responce?

## Double zero, let it ride

I'm wondering whether a randomized computation (Monte Carlo, etc.) has ever gotten a string of very unlucky random numbers, computed an erroneous result, and caused a real-world problem. [more inside]

## Given an average rate how do I calculate how often to do something?

I get seed packets that (usually) give a germination rate. How do I calculate how many seeds to plant to give me a 'y' probability of getting 'z' seeds to germinate? [more inside]

## 2 problems of combinations and permutations.

How many unique ways are there to put X rocks into Y boxes?
(Given two different sets of attributes for both the rocks and the boxes.) [more inside]

## Help me with a permutations probability problem.

I'm an answer-checker who is rusty at probability. Can you solve this problem?
What is the probability that a random arrangement of the letters in the word THRUSTS will have the two T's next to each other? [more inside]

## Chance of event with small sample size, based on larger related sample?

Can/how can one improve the estimate for a chance of an event with a small historical sample size by utilizing the chance of a related event with a large historical sample size? Example and half-assed guess inside. [more inside]

## The Gambler's Fallacy, of course. But maybe...

A coin flips three times and comes up heads 2/3. Not suspect.
But a coin flips 100,000 times and comes up heads 2 out of 3 times, that starts to look fishy. The standard probability of this is always roughly 50-50, but assuming a 2/3 ratio pointing to a "rigged" coin, how could you plot the increasing likelihood that a given coin is rigged? [more inside]

## Bad at math

I have a question about probability math. I am essentially flipping a coin (except instead of a 50/50 chance, my odds are 50.5% heads, 49.5% tails).
I am concerned with the probability of me hitting heads (a 50.5% chance) several times in a row. [more inside]

## Probability and a rather unique deck of cards.

Each card in a certain deck has three letters on it.
The first letter is either A, B, or C.
The second letter is either D, E, F, or G.
The third letter is either H, I, J, K, or L.
Every possible combination is represented exactly once in the deck. Ergo, there are 3x4x5=60 cards in the deck.
How can I determine the probability that a hand of X cards, drawn randomly from the deck, will include at least one of each of the letters?

## Very specific probability question

Hi guys:
I hope that the green can help me on this- perhaps it's an easy problem for you:
I have 9 different playing cards and 2 players. The first player can take between 3 to 5 cards and the remainder are given to the second player, and then the game begins.
How many different starting hands (collectively between the two players) are there? The order of the cards in each player's hand does not matter. Thanks in advance!

## I'm having trouble understanding likelihood ratios and diagnostic tests.

I'm struggling to understand likelihood ratios (LR) in the context of diagnostic tests, and why a positive LR is influenced by the sensitivity of the test. [more inside]

## Is there a name for this logical fallacy? It has to do with statistics.

The fallacy is assuming that statistic information about a thing is more relevant in dealing with a particular instance of that thing than available first-hand data. [more inside]

## What are the odds? Is intelligent design more plausible than chance?

I'm a cataloging librarian who works a couple hours a week on the reference desk. This morning I had a patron come in to ask me for sources that back up the claim that the probability that life on earth formed by random chance is so small that some kind of divine intervention is more likely. [more inside]

## Human Random Generator

Can you think of a method that allows an individual to pseudo randomly create a sequence of numbers (at the very least the randomness is opaque to the minds of other people) assuming said individual may only use his mind and body (no physical tools are allowed)? [more inside]

## What does a professional statistician do?

(Good) jobs involving probability and statistics other than math teacher or actuary? [more inside]

## How to solve a complex statistics problem with a script?

In this game, you roll a number of six-sided dice to get a

**total**. The total is either the highest single die result, or the sum of any multiples rolled, whichever is higher. For example: If I roll three dice and get a 3, 4, and 6, my total is 6. But if I roll a 4, 4, and 6, my total is 8, the sum of the two 4s. What I want to find out is the mean, median, mode, and standard deviation of the possible totals given N dice. How might I create a simple script to compute this? [more inside]## Practice Probability Word Problems

What great books or resources are there for practicing probability word problems such as for standardized tests like the GRE? [more inside]

## Explain something easy to me.

## What are the odds that two randomly selected people share the same bank PIN?

Statisticsfilter: Given available information about the distribution of self-selected 4-digit passwords (specifically banking PINs), is it possible to calculate the probability of two randomly selected individuals having the same PIN? If so, what're the odds? [more inside]

## How do I calculate the probability of a specific sum of repeated die rolls?

I'm looking to learn how to calculate probabilities for a multi-round dice game. I've researched this question some, and it looks like I might need to know how to use the multinomial distribution, but I can't find any good introductions. Please point me to the most layman-accessible educational material on this subject, and help me to help myself. [more inside]

## Gambling odds question

How would one (legally) take advantage of the change in odds of a given NFL team to win the Super Bowl? [more inside]

## What are the odds?

Math/probability not sports: I am not a gambler, but I am trying out a method of betting on sports with some initial success. At what point can I use the numbers to confidently assume that this is down to the system rather than luck? [more inside]

## A different fussy suitor from those I've met before

I'm working through an explanation/derivation of the secretary problem that I've never seen before. I know the eventual answer, and I understand most of the steps, but explain this to me like I'm an idiot: [more inside]

## Maximising randomness or success probability field blog post.

Looking for an interesting blog post somewhere from a few months back about maximising your exposure to randomness or your probability of a good outcome. Think it was a geek post somewhere. [more inside]

## Recommendations for great books about probability and risk.

Recommendations for great books about probability and risk. [more inside]

## Taking the random out of racking

After tens of thousands of games of pool, every time I rack the balls I seem to switch about half of them around. I know I'm wasting time. So, I want to know exactly how many balls I should

*normally*expect to swap (the median), and what is the most I should*ever have*to swap. For those of you who aren't pool nerds like me, I've explained the 8-ball racking process inside. [more inside]## Most 'realistic' rpg rules?

What are the most mathematically 'advanced' RPG systems? Pen & paper and otherwise? [more inside]

## Thirsty work

Mathfilter. Bonus: involves football and beer [more inside]

## New directions?

Where should I study philosophy? [more inside]

## Calculating the average wait time for a book on hold at the library (or "Why didn't they teach something useful like this in library school?"

Is there an equation for figuring out the average wait time for a book on hold at the library. Or how to figure out the average wait time I have left for a book I put on hold because I'm dying to read the rest of it. [more inside]

## Maximum number of outs on the river in holdem.

What is the maximum number of outs possible on the river in heads up Texas hold em? Assuming that out means a card which will take the player who is behind either level or ahead.

## Are probabilistic theories scientific?

I'm struggling to understand the empirical content of probability theory. I understand the mathematical theory, and I understand how we get from empirical observations to a mathematical model. I do not understand how we get from the mathematical model back to the real world, e.g., what is the "empirical content" of a statement like "event

*x*will occur with probability*p*"? [more inside]## Probability Question

Probability Question [more inside]

## Statistics filter: How do I calculate the keyspace size of a password?

How do I figure out what the size of this password's keyspace is? [more inside]

## Help me beat the odds.

How do you improve your odds of winning at a drawing with multiple prizes? [more inside]