How to calculate how lucky you are in a contest. Probability.
$begingroup$
You are on a beach full of rocks looking for treasure. The odds of finding treasure under any rock is $1/273$. You have looked under $5000$ rocks and found only $2$ pieces of treasure. How unlucky were you? What are the odds of looking under $5000$ rocks and finding only $2$ pieces of treasure (when the odds of looking under $1$ rock and finding treasure is $1/273$)? I assume you have to add the probability of finding $0$, $1$ and $2$ together?
I found this website, but the numbers aren't precise enough for me. I would like to convert the odds to something more manageable. I wanted to be able to say, this is equivalent to getting heads X number times in a row for coin tosses. And with my sample data it just turns into "$0.9999999$" on that site, so its not useful to me.
I think I need "Cumulative probability: $P(X ≤ x)$".
If someone could help explain it to me.
Ideally I would also like to know how much outside of the norm my sample set is. In other words, I question the validity of the 1/273 odds and want to know the best way to test it.
probability probability-distributions
$endgroup$
add a comment |
$begingroup$
You are on a beach full of rocks looking for treasure. The odds of finding treasure under any rock is $1/273$. You have looked under $5000$ rocks and found only $2$ pieces of treasure. How unlucky were you? What are the odds of looking under $5000$ rocks and finding only $2$ pieces of treasure (when the odds of looking under $1$ rock and finding treasure is $1/273$)? I assume you have to add the probability of finding $0$, $1$ and $2$ together?
I found this website, but the numbers aren't precise enough for me. I would like to convert the odds to something more manageable. I wanted to be able to say, this is equivalent to getting heads X number times in a row for coin tosses. And with my sample data it just turns into "$0.9999999$" on that site, so its not useful to me.
I think I need "Cumulative probability: $P(X ≤ x)$".
If someone could help explain it to me.
Ideally I would also like to know how much outside of the norm my sample set is. In other words, I question the validity of the 1/273 odds and want to know the best way to test it.
probability probability-distributions
$endgroup$
$begingroup$
Regarding the question toward the end of your post: If you toss a coin $10$ times, you will always have $le 10$ heads.
$endgroup$
– angryavian
Dec 31 '18 at 1:39
$begingroup$
"How unlucky were you?" -- Unless you have a means of quantifying this, no one is going to be able to help you on that. (Unless it's a more colloquial statement answered by the others.)
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:41
$begingroup$
As for the fact that the calculators seem to be producing $100%$ or something of the sort, that's an artifact of how small the odds of this happening are, and the fact that the average program/calculator/whatever cannot readily calculate something to such a precision, so it just rounds as close as it can get. You will have to calculate it manually using the binomial distribution formulas if you want a more precise answer.
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:43
$begingroup$
Just use the binomial distribution with $p=frac 1{273}$. We get $P(X=0)+P(X=1)+P(X=2)=.00000202369$ so you would indeed have to be very unlucky not to have more than $2$ successes. The expected number of wins is $frac {5000}{273}=18.315$
$endgroup$
– lulu
Dec 31 '18 at 1:44
add a comment |
$begingroup$
You are on a beach full of rocks looking for treasure. The odds of finding treasure under any rock is $1/273$. You have looked under $5000$ rocks and found only $2$ pieces of treasure. How unlucky were you? What are the odds of looking under $5000$ rocks and finding only $2$ pieces of treasure (when the odds of looking under $1$ rock and finding treasure is $1/273$)? I assume you have to add the probability of finding $0$, $1$ and $2$ together?
I found this website, but the numbers aren't precise enough for me. I would like to convert the odds to something more manageable. I wanted to be able to say, this is equivalent to getting heads X number times in a row for coin tosses. And with my sample data it just turns into "$0.9999999$" on that site, so its not useful to me.
I think I need "Cumulative probability: $P(X ≤ x)$".
If someone could help explain it to me.
Ideally I would also like to know how much outside of the norm my sample set is. In other words, I question the validity of the 1/273 odds and want to know the best way to test it.
probability probability-distributions
$endgroup$
You are on a beach full of rocks looking for treasure. The odds of finding treasure under any rock is $1/273$. You have looked under $5000$ rocks and found only $2$ pieces of treasure. How unlucky were you? What are the odds of looking under $5000$ rocks and finding only $2$ pieces of treasure (when the odds of looking under $1$ rock and finding treasure is $1/273$)? I assume you have to add the probability of finding $0$, $1$ and $2$ together?
I found this website, but the numbers aren't precise enough for me. I would like to convert the odds to something more manageable. I wanted to be able to say, this is equivalent to getting heads X number times in a row for coin tosses. And with my sample data it just turns into "$0.9999999$" on that site, so its not useful to me.
I think I need "Cumulative probability: $P(X ≤ x)$".
If someone could help explain it to me.
Ideally I would also like to know how much outside of the norm my sample set is. In other words, I question the validity of the 1/273 odds and want to know the best way to test it.
probability probability-distributions
probability probability-distributions
edited Dec 31 '18 at 2:53
Curtis
asked Dec 31 '18 at 1:35
CurtisCurtis
1064
1064
$begingroup$
Regarding the question toward the end of your post: If you toss a coin $10$ times, you will always have $le 10$ heads.
$endgroup$
– angryavian
Dec 31 '18 at 1:39
$begingroup$
"How unlucky were you?" -- Unless you have a means of quantifying this, no one is going to be able to help you on that. (Unless it's a more colloquial statement answered by the others.)
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:41
$begingroup$
As for the fact that the calculators seem to be producing $100%$ or something of the sort, that's an artifact of how small the odds of this happening are, and the fact that the average program/calculator/whatever cannot readily calculate something to such a precision, so it just rounds as close as it can get. You will have to calculate it manually using the binomial distribution formulas if you want a more precise answer.
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:43
$begingroup$
Just use the binomial distribution with $p=frac 1{273}$. We get $P(X=0)+P(X=1)+P(X=2)=.00000202369$ so you would indeed have to be very unlucky not to have more than $2$ successes. The expected number of wins is $frac {5000}{273}=18.315$
$endgroup$
– lulu
Dec 31 '18 at 1:44
add a comment |
$begingroup$
Regarding the question toward the end of your post: If you toss a coin $10$ times, you will always have $le 10$ heads.
$endgroup$
– angryavian
Dec 31 '18 at 1:39
$begingroup$
"How unlucky were you?" -- Unless you have a means of quantifying this, no one is going to be able to help you on that. (Unless it's a more colloquial statement answered by the others.)
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:41
$begingroup$
As for the fact that the calculators seem to be producing $100%$ or something of the sort, that's an artifact of how small the odds of this happening are, and the fact that the average program/calculator/whatever cannot readily calculate something to such a precision, so it just rounds as close as it can get. You will have to calculate it manually using the binomial distribution formulas if you want a more precise answer.
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:43
$begingroup$
Just use the binomial distribution with $p=frac 1{273}$. We get $P(X=0)+P(X=1)+P(X=2)=.00000202369$ so you would indeed have to be very unlucky not to have more than $2$ successes. The expected number of wins is $frac {5000}{273}=18.315$
$endgroup$
– lulu
Dec 31 '18 at 1:44
$begingroup$
Regarding the question toward the end of your post: If you toss a coin $10$ times, you will always have $le 10$ heads.
$endgroup$
– angryavian
Dec 31 '18 at 1:39
$begingroup$
Regarding the question toward the end of your post: If you toss a coin $10$ times, you will always have $le 10$ heads.
$endgroup$
– angryavian
Dec 31 '18 at 1:39
$begingroup$
"How unlucky were you?" -- Unless you have a means of quantifying this, no one is going to be able to help you on that. (Unless it's a more colloquial statement answered by the others.)
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:41
$begingroup$
"How unlucky were you?" -- Unless you have a means of quantifying this, no one is going to be able to help you on that. (Unless it's a more colloquial statement answered by the others.)
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:41
$begingroup$
As for the fact that the calculators seem to be producing $100%$ or something of the sort, that's an artifact of how small the odds of this happening are, and the fact that the average program/calculator/whatever cannot readily calculate something to such a precision, so it just rounds as close as it can get. You will have to calculate it manually using the binomial distribution formulas if you want a more precise answer.
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:43
$begingroup$
As for the fact that the calculators seem to be producing $100%$ or something of the sort, that's an artifact of how small the odds of this happening are, and the fact that the average program/calculator/whatever cannot readily calculate something to such a precision, so it just rounds as close as it can get. You will have to calculate it manually using the binomial distribution formulas if you want a more precise answer.
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:43
$begingroup$
Just use the binomial distribution with $p=frac 1{273}$. We get $P(X=0)+P(X=1)+P(X=2)=.00000202369$ so you would indeed have to be very unlucky not to have more than $2$ successes. The expected number of wins is $frac {5000}{273}=18.315$
$endgroup$
– lulu
Dec 31 '18 at 1:44
$begingroup$
Just use the binomial distribution with $p=frac 1{273}$. We get $P(X=0)+P(X=1)+P(X=2)=.00000202369$ so you would indeed have to be very unlucky not to have more than $2$ successes. The expected number of wins is $frac {5000}{273}=18.315$
$endgroup$
– lulu
Dec 31 '18 at 1:44
add a comment |
1 Answer
1
active
oldest
votes
$begingroup$
"More precise" isn't necessarily the right viewpoint here, especially when you're having issues with a theoretically accurate calculation rounding to $0$ or $1$. Instead, we should look for an approximate model that handles this extreme well.
And on that note - there is such a model. The Poisson distribution arises as a limit of binomial distributions with large numbers of trials, low probability, and fixed mean. That mean becomes the distribution's sole parameter $lambda$, which will be $frac{5000}{273}approx 18.315$ in this case.
In a Poisson distribution with parameter $lambda$, the probability of getting exactly $k$ is $frac{lambda^k}{k!}e^{-k}$. Here, that gives (using Excel for the calculations, since I happen to have it open), probabilities of 1.11145E-08 for $0$, 2.03562E-07 for $1$, and 1.86412E-06 for $2$. The probability of being at most $2$ is their sum 2.07879E-06.
Well, OK, we don't really have all of those digits - but it'll be pretty close. We can confidently say that if the probabilities were accurate, the likelihood of getting at most two successes would be approximately $2cdot 10^{-6}$. That's definitely a "reject the hypothesis" level.
How many consecutive head flips would it take to reach that level of unlikeliness? The probability of $n$ consecutive flips (with no extra tries) is $2^{-n}$. From the standard approximation $2^{10}approx 10^3$, we get $10^{-6}approx 2^{-20}$, and $2^{-19}approx 2cdot 10^{-6}$. It would take nineteen consecutive head flips to reach that level of improbability.
I tried a manual version of the binomial approximation as well - it came out about $2.5%$ different, a total probability of about $2.024cdot 10^{-6}$. It's technically more accurate, but is that worth switching from a simple exponential $e^{-lambda}$ to a high power $(1-p)^N$ of something very close to $1$?
$endgroup$
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "69"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3057364%2fhow-to-calculate-how-lucky-you-are-in-a-contest-probability%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
$begingroup$
"More precise" isn't necessarily the right viewpoint here, especially when you're having issues with a theoretically accurate calculation rounding to $0$ or $1$. Instead, we should look for an approximate model that handles this extreme well.
And on that note - there is such a model. The Poisson distribution arises as a limit of binomial distributions with large numbers of trials, low probability, and fixed mean. That mean becomes the distribution's sole parameter $lambda$, which will be $frac{5000}{273}approx 18.315$ in this case.
In a Poisson distribution with parameter $lambda$, the probability of getting exactly $k$ is $frac{lambda^k}{k!}e^{-k}$. Here, that gives (using Excel for the calculations, since I happen to have it open), probabilities of 1.11145E-08 for $0$, 2.03562E-07 for $1$, and 1.86412E-06 for $2$. The probability of being at most $2$ is their sum 2.07879E-06.
Well, OK, we don't really have all of those digits - but it'll be pretty close. We can confidently say that if the probabilities were accurate, the likelihood of getting at most two successes would be approximately $2cdot 10^{-6}$. That's definitely a "reject the hypothesis" level.
How many consecutive head flips would it take to reach that level of unlikeliness? The probability of $n$ consecutive flips (with no extra tries) is $2^{-n}$. From the standard approximation $2^{10}approx 10^3$, we get $10^{-6}approx 2^{-20}$, and $2^{-19}approx 2cdot 10^{-6}$. It would take nineteen consecutive head flips to reach that level of improbability.
I tried a manual version of the binomial approximation as well - it came out about $2.5%$ different, a total probability of about $2.024cdot 10^{-6}$. It's technically more accurate, but is that worth switching from a simple exponential $e^{-lambda}$ to a high power $(1-p)^N$ of something very close to $1$?
$endgroup$
add a comment |
$begingroup$
"More precise" isn't necessarily the right viewpoint here, especially when you're having issues with a theoretically accurate calculation rounding to $0$ or $1$. Instead, we should look for an approximate model that handles this extreme well.
And on that note - there is such a model. The Poisson distribution arises as a limit of binomial distributions with large numbers of trials, low probability, and fixed mean. That mean becomes the distribution's sole parameter $lambda$, which will be $frac{5000}{273}approx 18.315$ in this case.
In a Poisson distribution with parameter $lambda$, the probability of getting exactly $k$ is $frac{lambda^k}{k!}e^{-k}$. Here, that gives (using Excel for the calculations, since I happen to have it open), probabilities of 1.11145E-08 for $0$, 2.03562E-07 for $1$, and 1.86412E-06 for $2$. The probability of being at most $2$ is their sum 2.07879E-06.
Well, OK, we don't really have all of those digits - but it'll be pretty close. We can confidently say that if the probabilities were accurate, the likelihood of getting at most two successes would be approximately $2cdot 10^{-6}$. That's definitely a "reject the hypothesis" level.
How many consecutive head flips would it take to reach that level of unlikeliness? The probability of $n$ consecutive flips (with no extra tries) is $2^{-n}$. From the standard approximation $2^{10}approx 10^3$, we get $10^{-6}approx 2^{-20}$, and $2^{-19}approx 2cdot 10^{-6}$. It would take nineteen consecutive head flips to reach that level of improbability.
I tried a manual version of the binomial approximation as well - it came out about $2.5%$ different, a total probability of about $2.024cdot 10^{-6}$. It's technically more accurate, but is that worth switching from a simple exponential $e^{-lambda}$ to a high power $(1-p)^N$ of something very close to $1$?
$endgroup$
add a comment |
$begingroup$
"More precise" isn't necessarily the right viewpoint here, especially when you're having issues with a theoretically accurate calculation rounding to $0$ or $1$. Instead, we should look for an approximate model that handles this extreme well.
And on that note - there is such a model. The Poisson distribution arises as a limit of binomial distributions with large numbers of trials, low probability, and fixed mean. That mean becomes the distribution's sole parameter $lambda$, which will be $frac{5000}{273}approx 18.315$ in this case.
In a Poisson distribution with parameter $lambda$, the probability of getting exactly $k$ is $frac{lambda^k}{k!}e^{-k}$. Here, that gives (using Excel for the calculations, since I happen to have it open), probabilities of 1.11145E-08 for $0$, 2.03562E-07 for $1$, and 1.86412E-06 for $2$. The probability of being at most $2$ is their sum 2.07879E-06.
Well, OK, we don't really have all of those digits - but it'll be pretty close. We can confidently say that if the probabilities were accurate, the likelihood of getting at most two successes would be approximately $2cdot 10^{-6}$. That's definitely a "reject the hypothesis" level.
How many consecutive head flips would it take to reach that level of unlikeliness? The probability of $n$ consecutive flips (with no extra tries) is $2^{-n}$. From the standard approximation $2^{10}approx 10^3$, we get $10^{-6}approx 2^{-20}$, and $2^{-19}approx 2cdot 10^{-6}$. It would take nineteen consecutive head flips to reach that level of improbability.
I tried a manual version of the binomial approximation as well - it came out about $2.5%$ different, a total probability of about $2.024cdot 10^{-6}$. It's technically more accurate, but is that worth switching from a simple exponential $e^{-lambda}$ to a high power $(1-p)^N$ of something very close to $1$?
$endgroup$
"More precise" isn't necessarily the right viewpoint here, especially when you're having issues with a theoretically accurate calculation rounding to $0$ or $1$. Instead, we should look for an approximate model that handles this extreme well.
And on that note - there is such a model. The Poisson distribution arises as a limit of binomial distributions with large numbers of trials, low probability, and fixed mean. That mean becomes the distribution's sole parameter $lambda$, which will be $frac{5000}{273}approx 18.315$ in this case.
In a Poisson distribution with parameter $lambda$, the probability of getting exactly $k$ is $frac{lambda^k}{k!}e^{-k}$. Here, that gives (using Excel for the calculations, since I happen to have it open), probabilities of 1.11145E-08 for $0$, 2.03562E-07 for $1$, and 1.86412E-06 for $2$. The probability of being at most $2$ is their sum 2.07879E-06.
Well, OK, we don't really have all of those digits - but it'll be pretty close. We can confidently say that if the probabilities were accurate, the likelihood of getting at most two successes would be approximately $2cdot 10^{-6}$. That's definitely a "reject the hypothesis" level.
How many consecutive head flips would it take to reach that level of unlikeliness? The probability of $n$ consecutive flips (with no extra tries) is $2^{-n}$. From the standard approximation $2^{10}approx 10^3$, we get $10^{-6}approx 2^{-20}$, and $2^{-19}approx 2cdot 10^{-6}$. It would take nineteen consecutive head flips to reach that level of improbability.
I tried a manual version of the binomial approximation as well - it came out about $2.5%$ different, a total probability of about $2.024cdot 10^{-6}$. It's technically more accurate, but is that worth switching from a simple exponential $e^{-lambda}$ to a high power $(1-p)^N$ of something very close to $1$?
answered Dec 31 '18 at 2:28
jmerryjmerry
16.1k1633
16.1k1633
add a comment |
add a comment |
Thanks for contributing an answer to Mathematics Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fmath.stackexchange.com%2fquestions%2f3057364%2fhow-to-calculate-how-lucky-you-are-in-a-contest-probability%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
$begingroup$
Regarding the question toward the end of your post: If you toss a coin $10$ times, you will always have $le 10$ heads.
$endgroup$
– angryavian
Dec 31 '18 at 1:39
$begingroup$
"How unlucky were you?" -- Unless you have a means of quantifying this, no one is going to be able to help you on that. (Unless it's a more colloquial statement answered by the others.)
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:41
$begingroup$
As for the fact that the calculators seem to be producing $100%$ or something of the sort, that's an artifact of how small the odds of this happening are, and the fact that the average program/calculator/whatever cannot readily calculate something to such a precision, so it just rounds as close as it can get. You will have to calculate it manually using the binomial distribution formulas if you want a more precise answer.
$endgroup$
– Eevee Trainer
Dec 31 '18 at 1:43
$begingroup$
Just use the binomial distribution with $p=frac 1{273}$. We get $P(X=0)+P(X=1)+P(X=2)=.00000202369$ so you would indeed have to be very unlucky not to have more than $2$ successes. The expected number of wins is $frac {5000}{273}=18.315$
$endgroup$
– lulu
Dec 31 '18 at 1:44