Chris Chiu wrote:
>
> Dear friends:
>
> Does anyone know / remember how to obtain the standard deviation of a set
> of numbers given only a frequency table?
>
> e.g.,
> x f(x)
> 0 0.2
> 1 0.3
> 2 0.2
> 3 0.2
> 4 0.1
>
> Many thanks.
> Chris
>
calculate average value "a"
change your "f(x)" into "f", which is number of observation in the given
row of the frequency table. Sum of "f" from all rows equals "n" (number
of observations).
s = sqr { [sum(f*(x-a)^2)] / [n-1] }
Have gave more brackets than necessary to make the formula more clear (i
hope :-)
Fowler J, Cohen L, Jarvis P 1998. Practical statistics for field
biology. Wiley, page 38.
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