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    Thought S4 would be hard having not looked at it at all until today (too many other exams!), but it doesn't seem to bad in truth. Really helps that there's so much overlap with AQA Statistics too, as I have S4 and SS05 on the same day >.<
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    (Original post by angrybirdzzz)
    Thought S4 would be hard having not looked at it at all until today (too many other exams!), but it doesn't seem to bad in truth. Really helps that there's so much overlap with AQA Statistics too, as I have S4 and SS05 on the same day >.<
    Yeah, it's not sooo bad though out of interest, how/why are you doing SS05?
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    (Original post by SeanFM)
    Yeah, it's not sooo bad though out of interest, how/why are you doing SS05?
    Doing all 18 Edexcel modules on top of the 6 AQA Statistics ones. People say it's a waste of time, I say it's a challenge
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    (Original post by angrybirdzzz)
    Doing all 18 Edexcel modules on top of the 6 AQA Statistics ones. People say it's a waste of time, I say it's a challenge
    Fairs I wouldn't think you're sitting all 24 in one year, but that is still a bit.. stressful
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    (Original post by SeanFM)
    Fairs I wouldn't think you're sitting all 24 in one year, but that is still a bit.. stressful
    Yeah, did C1-4, S1-2 and SS1B-03 last year.

    I know people who have to retake S2 and have a triple FP3, SS06 and S2 retake clash next Monday! :bricks:
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    (Original post by SeanFM)
    Please link the paper
    https://7c9a99abd139eb14bde7da77d86a...%20Edexcel.pdf
    Hope it works. It's on Physics and Maths tutor.
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    Would anyone be able to give me a hint for this one? I don't know how to work with the sums of X^2 that come with S^2 etc.

    And does anyone know why they gave me information about a chi-square variable? :lol:

    SeanFM
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    (Original post by 130398)
    https://7c9a99abd139eb14bde7da77d86a...%20Edexcel.pdf
    Hope it works. It's on Physics and Maths tutor.
    Well.. starting with 7, what have you tried/thought about?
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    (Original post by Euclidean)
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    Would anyone be able to give me a hint for this one? I don't know how to work with the sums of X^2 that come with S^2 etc.

    And does anyone know why they gave me information about a chi-square variable? :lol:

    SeanFM
    I've gotta be honest, I'm not sure on this one. :hide: I've had a look at all of the definitions and stuff but can't really think of what to do.

    It might have something to do with this: if it comes up in S4..
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    (Original post by SeanFM)
    Well.. starting with 7, what have you tried/thought about?
    Please don't. I don't understand why they used the Critical value equation from part a) and used another one in b) (with mu=200 and z=1.6449). I got the numbers but I didn't understand what to do with them. How would I calculate P(type II error) in this specific case (not the general definition of accepting Ho when it's false).
    8 I started to understand.
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    (Original post by SeanFM)
    I've gotta be honest, I'm not sure on this one. :hide: I've had a look at all of the definitions and stuff but can't really think of what to do.

    It might have something to do with this: if it comes up in S4..
    PRSOM.

    70% of S4 makes sense to me about now, I'm gonna leave it at that. Make sure I get that 82 in C4 now :lol:
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    (Original post by 130398)
    Please don't. I don't understand why they used the Critical value equation from part a) and used another one in b) (with mu=200 and z=1.6449). I got the numbers but I didn't understand what to do with them. How would I calculate P(type II error) in this specific case (not the general definition of accepting Ho when it's false).
    8 I started to understand.
    If you don't tell me where or how you're stuck, I would just be parroting what the mark scheme would say, or waste a lot of time going into detail over the question and I'm not here to waste my time.

    The question is rather confusing because you're used to say, it looking like power functions (or the power function evaluated at a specific point), rather than doing it in terms of the critical value. (once you've got the expression for the probability of type two errors, you've got two equations to solve simultaneously but I think it's the bit before that that is troubling you.

    Remember that the CV is a test statistic, and to get a type two error, you have to accept the hypothesis given that it is not true, so the 'accept the hypothesis' part comes from the test statistic falling outside the critical region and the 'given that it is not true' part comes from having mu as the actual value rather than the one in the hypothesis (i.e 200 instead of 202).

    So the probability of getting the CV or less, given that mu is 200, is less than 0.05 (which corresponds to a z value of 1.6449), and so the z value corresponds to CV - 200 / (2/sqrtn). You can think of it as a distribution where you've changed the mean because you're looking for the probability of a type 2 error at a specified mean, but carrying over the old test statistic (because that's when you accept/reject the test erroneously) and looking for P(X=< CV), where X~N(200,2/sqrt2).
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    (Original post by SeanFM)
    I've gotta be honest, I'm not sure on this one. :hide: I've had a look at all of the definitions and stuff but can't really think of what to do.

    It might have something to do with this: if it comes up in S4..
    Suggested solution: It is necessary to first show that S^2 is an unbiased estimator of sigma squared. By rearranging the equation above to make S^2 the subject we get: (Chi squared)(sigma squared)/(n-1), the chi squared variable can be replaced by the random variable Y.

    It is known that E(Y) = V, therefore:

    E(S^2) = E(Y)(sigma squared)/(n-1) = V(sigma squared)/(n-1)

    In general V = degrees of freedom = n-1.
    Replacing V with n-1:
    E(S^2)= (n-1)(sigma squared)/(n-1)
    Common terms n-1 cancel out. Hence E(S^2) = sigma squared is an unbiased estimator.

    Using the same idea, Var(S^2) can be calculated to be equal to:
    2(sigma)^4/(n-1). Following this, as n approaches infinity, the variance of S^2 approaches zero. It is therefore a consistent estimator.

    In general, we can use the chi squared variable Y to derive the properties of S^2.
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    (Original post by A Question)
    Suggested solution: It is necessary to first show that S^2 is an unbiased estimator of sigma squared. By rearranging the equation above to make S^2 the subject we get: (Chi squared)(sigma squared)/(n-1), the chi squared variable can be replaced by the random variable Y.

    It is known that E(Y) = V, therefore:

    E(S^2) = E(Y)(sigma squared)/(n-1) = V(sigma squared)/(n-1)

    In general V = degrees of freedom = n-1.
    Replacing V with n-1:
    E(S^2)= (n-1)(sigma squared)/(n-1)
    Common terms n-1 cancel out. Hence E(S^2) = sigma squared is an unbiased estimator.

    Using the same idea, Var(S^2) can be calculated to be equal to:
    2(sigma)^4/(n-1). Following this, as n approaches infinity, the variance of S^2 approaches zero. It is therefore a consistent estimator.

    In general, we can use the chi squared variable Y to derive the properties of S^2.
    Nice one. Thanks for that

    I would've thought it wasn't necessary to show that it was unbiased (i.e irrespective of whether it is unbiased or not, it can still be consistent?)
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    (Original post by SeanFM)
    Nice one. Thanks for that

    I would've thought it wasn't necessary to show that it was unbiased (i.e irrespective of whether it is unbiased or not, it can still be consistent?)
    you always gotta do the bias test - otherwise it is an unsuitable estimator.
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    https://7c9a99abd139eb14bde7da77d86a...%20Edexcel.pdf

    Qn 4 part c i actually don't understand where to begin - I drew out a table of probabilities but then it got me no where (unless i did it wrong...which i doubt)
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    (Original post by tazza ma razza)
    you always gotta do the bias test - otherwise it is an unsuitable estimator.
    Yeah, it would be unsuitable but it could still be consistent? It's just asking for consistency rather than comparing estimators or checking if this one is suitable/not, unless I'm missing something
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    (Original post by tazza ma razza)
    https://7c9a99abd139eb14bde7da77d86a...%20Edexcel.pdf

    Qn 4 part c i actually don't understand where to begin - I drew out a table of probabilities but then it got me no where (unless i did it wrong...which i doubt)
    Use the definition of expectation in the discrete case (where you write all the values that it can take, and multiply it by the probability) i.e  E(X) = x_1 P(X=x_1) + x_2 P(X=x_2)....

    How you do that is by interpreting the different number of eggs that can be inspected, depending on 'how things go down' so to speak, and their corresponding probabilities.
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    (Original post by SeanFM)
    Use the definition of expectation in the discrete case (where you write all the values that it can take, and multiply it by the probability) i.e  E(X) = x_1 P(X=x_1) + x_2 P(X=x_2)....
    dammit i was so close!
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    apart from june 11, what is a hard paper?

    I think grade boundaries will be:

    100 - 75
    90 - 69
    80 - 64
 
 
 
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