Standard Deviation Formula
Standard Deviation is the measure which tells us how scores are spread around the mean. In-other-words how much the scores “deviate” from the mean.There are 2 formulae for calculating the standard deviation:
They may look pretty complicated, but in fact are pretty easy to use, especially the second one which is the more widely used.
Example:
To find the standard deviation of this set of numbers:
3, 5, 5, 7, 9
We will need the mean to calculate the standard deviation where:
The smaller the standard deviation (e.g. 2.1), the closer together the values in the set are. A larger standard deviation (e.g. 5.1) shows that the values are more spread out from the mean.
The advantage is that all scores in the set are taken into account so it is more accurate than the range and it can also be used in further analysis / calculations. The disadvantage is it is not as quick or easy to calculate than other measures of dispersion, such as the range (i.e. time consuming).
Statistics PDF Downloads