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Math Help - Variance and sample size

  1. #1
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    Variance and sample size

    Could someone please explain to me the relationship between variance and sample size. i know that when the sample is small the variance larger (hence, we use students t distribution when estimating small samples). but why exactly is this? i saw a question in a past paper, asking whether or not a large sample will have a smaller variance compared to a smaller sample and i was not sure how to answer. please help!
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  2. #2
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    Quote Originally Posted by star_Asia View Post
    Could someone please explain to me the relationship between variance and sample size. i know that when the sample is small the variance larger (hence, we use students t distribution when estimating small samples). but why exactly is this? i saw a question in a past paper, asking whether or not a large sample will have a smaller variance compared to a smaller sample and i was not sure how to answer. please help!
    The variance of a sample is a random variable which can be used as an
    estimator of the population variance (and will be unbiased if the correct
    variant is used). As such it is approximatly equal to the population
    variance, and the approximation is (probably) better for a larger sample
    than for a smaller sample.

    The variance of the mean of a sample is what gets smaller as the sample
    size goes up, and this variance is inversly proportional to the square
    root of the sample size.

    RonL
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