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    Ancient Orator leehuan's Avatar
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    Statistics

    It's a geometric distribution but suppose we didn't know that




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    Re: Statistics

    Quote Originally Posted by leehuan View Post
    It's a geometric distribution but suppose we didn't know that



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    Re: Statistics

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    Re: Statistics

    ELI5 Please
    BCom acct/fins @UNSW

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    Re: Statistics

    Quote Originally Posted by Confound View Post
    ELI5 Please
    Explain what? Every single detail? InteGrand's sum derivation?

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    Ancient Orator leehuan's Avatar
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    Re: Statistics

    Quick question regarding probability spaces:


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    Re: Statistics

    Quote Originally Posted by leehuan View Post
    Quick question regarding probability spaces:

    Greater than or equal to. Events can have 0 probability.
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    Re: Statistics

    leehuan - what would you do if InteGrand decides to take a 6 month sabbatical?
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    Ancient Orator leehuan's Avatar
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    Re: Statistics

    Quote Originally Posted by Drongoski View Post
    leehuan - what would you do if InteGrand decides to take a 6 month sabbatical?
    I don't know; InteGrand can do as he wants. But why are you asking me this?
    Last edited by leehuan; 6 Mar 2017 at 12:47 PM.

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    Re: Statistics

    Quote Originally Posted by leehuan View Post
    I don't know; InteGrand can do as he wants. But why are you asking me this?
    Just teasing you. And noting that InteGrand has been helping you so much.
    Last edited by Drongoski; 6 Mar 2017 at 2:00 PM.
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    Ancient Orator leehuan's Avatar
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    Re: Statistics

    Quote Originally Posted by Drongoski View Post
    Just teasing you. And noting that InteGrand has been helping you so much.
    Very true. So grateful.

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    Ancient Orator leehuan's Avatar
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    Re: Statistics

    I wasn't taught the hypergeometric distribution properly so can someone walk me through how to use it? Here's my question if it helps to refer to it.



    A factory produces 80 items in a batch. To test if the batch is defective, an acceptance sampling scheme is adopted: a random sample of 10 items is selected, and if 2 or more items don’t meet customer specifications, the batch is considered defective.

    If there are actually 11 defective items in the batch,

    1i) What is the probability that 2 sampled items are defective?
    ii) What is a general formula for x sampled items being defective?

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    Re: Statistics

    Doing this for the first time for a very very long long time. Not sure if correct.

    Last edited by Drongoski; 21 Mar 2017 at 2:25 PM.
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    Ancient Orator leehuan's Avatar
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    Re: Statistics

    Quote Originally Posted by Drongoski View Post
    Doing this for the first time for a very very long long time. Not sure if correct.

    I think the expressions are right.

    But I'm not sure what the parameters mean either. This question is pretty much an example but for an arbitrary scenario how would I be able to tell what the parameters (N, K, n) actually meant?

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    Re: Statistics

    Quote Originally Posted by leehuan View Post
    I think the expressions are right.

    But I'm not sure what the parameters mean either. This question is pretty much an example but for an arbitrary scenario how would I be able to tell what the parameters (N, K, n) actually meant?
    The parameters are as follows:

    • N is the total population
    • K is the number of "tagged" objects (defective objects in your example)
    • n is the size of our sample.

    The hypergeometric distribution pmf Drongoski wrote (in terms of the parameters N, K, n) then gives the probability that our sample has exactly k "tagged" (defective) objects present, under the assumption that we are sampling without replacement. This follows from basic combinatorics.
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    Re: Statistics

    The reason for terms like "population" and "tagged" is that one place this distribution comes up is in ecology when we tag some members of an animal population (like a fish population) and then later draw (without replacement) a random sample from the animal population and count how many are tagged. This can be used to try and estimate the total population for example (it is sometimes known as the "capture-recapture method", and you can read more about it here: https://en.wikipedia.org/wiki/Mark_and_recapture).
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    Re: Statistics

    Any tips for catching up on stats... like any resources you use?

    Thanks I am behind lol.
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    Ancient Orator leehuan's Avatar
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    Re: Statistics

    Can't deny it. I'm also a fair bit behind.

    Been cramming a lot of the course pack tbh.

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    Re: Statistics

    Quote Originally Posted by leehuan View Post
    Can't deny it. I'm also a fair bit behind.

    Been cramming a lot of the course pack tbh.
    what course pack? the questions that are on moodle or?
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    Ancient Orator leehuan's Avatar
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    Re: Statistics

    Quote Originally Posted by Flop21 View Post
    what course pack? the questions that are on moodle or?
    Course pack is just what I use to call the online 'textbook' thing. It's like what we had in first year except it's just not printed.

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    Supreme Member Flop21's Avatar
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    Re: Statistics

    is there an easy way to find the probability mass function??

    right now im just looking at example P(X=x) like P(X=1... etc.) and trying to find a pattern

    but this is hard for tricky ones
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    Re: Statistics

    Quote Originally Posted by Flop21 View Post
    is there an easy way to find the probability mass function??

    right now im just looking at example P(X=x) like P(X=1... etc.) and trying to find a pattern

    but this is hard for tricky ones
    Got an example question?

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    Re: Statistics

    Quote Originally Posted by He-Mann View Post
    Got an example question?
    A box contains four red and two black balls. Two balls are drawn. Let X be
    the number of red balls obtained. Find fX(x)


    Okay so if I haven't screwed up, P(X=0) = 1/15, P(X=1) = 4/5, P(X=2) = 2/5, and any other value of X, P = 0.

    So how do I put this into a proper answer for this question?
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    Re: Statistics

    Quote Originally Posted by Flop21 View Post
    A box contains four red and two black balls. Two balls are drawn. Let X be
    the number of red balls obtained. Find fX(x)


    Okay so if I haven't screwed up, P(X=0) = 1/15, P(X=1) = 4/5, P(X=2) = 2/5, and any other value of X, P = 0.

    So how do I put this into a proper answer for this question?










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    Supreme Member Flop21's Avatar
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    Re: Statistics

    Quote Originally Posted by InteGrand View Post










    yeah whoops typo'd something in my calculations so that stuffed up,

    so your final sentence, is that enough for an answer or do I need to know how to put it in a form with x ?
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