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Measures of dispersion – ACCA MA

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  2. Dear John,

    The Formula sheet provides 2 Formulas to Calculate Standard Deviation;

    You have Used the 1st one in this lecture: ?= ??(????)2 ÷ n

    Can we use the 2nd one: ?= ?(? ??² ÷ ? ?) ? (? ?? ÷ ? ?)²
    in arriving at the same answer at the Examination?

  6. Hello Sir
    First of all, thank you so much for the wonderful lessons
    You explain very nicely why when we want to know what is the VARIANCE we need to make the numbers SQUARED because if you did not turn them then the plus would balance with the minus and we would reach zero
    My question is this: after all, the numbers are supposed to be equal on both sides of the arithmetic mean, so why can we not just take only one side of the ARITHMETIC MEAN and divide it by only half the amount and then we were supposed to get a fair result???
    post Scriptum. I tried it on my calculator and came up with a different result

    • What you suggest would be a measure of spread (and will give a different result) but is not one that we ever use, because there is no further use for it.
      The variance and from it the standard deviation are useful in normal distribution theory as is explained in my lectures on the normal distribution.

  7. Hi John, how do we know when to use the formula for population variance and when to use the formula for sample variance? I.e. when do we know to divide just by n or by n-1 when calculating variance? TIA!

    • There are none. However there will be lots of questions in your Revision Kit (and it is absolutely essential that you have a Revision Kit from one of the ACCA approved publishers because they are full of exam standard questions for practice).

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