Mean, Variance and Standard Deviation by variablepitch346

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									Mean, Variance and Standard Deviation

Data List

Frequency Distribution

x

x n
2

Mean

x

fx f
2

 x  x  s  n 2 x s2   x2 n
2

Variance

 f x  x  s  f  fx 2 s2   x2 f
2

x 2 s  x2 n

Standard Deviation

s

 fx2  x2 f

To find representative values for grouped continuous data   Check that classes are continuous and, if necessary, find class boundaries. If classes are open-ended, select a ‘lower boundary’ for the first class or an ‘upper boundary’ for the last class.



Find the mid-class values. Usually mid-class value = 0.5 ( lower class boundary + upper class boundary )



Remember that mid-class values for disjoint age classes are calculated differently e.g. 15 – 29 people who are 15, 16, 17, …. 28, 29 midpoint = 0.5 ( 15 + 30 ) 30 – 39 people who are 30, 31, 32, ….. 38, 39 midpoint = 0.5 ( 30 + 40 )


								
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