Standard Deviation

Standard deviation is a measure of how spread out the values in a dataset are. In biology, it’s useful for showing variation in data such as heights, leaf lengths, or population sizes.

Where:

• x = each data value
• x̄ = mean of all values
• n = number of values

Worked Example

Calculate standard deviation for this dataset of leaf lengths (in cm):

x	x - x̄	(x - x̄)2
4	-1	1
6	1	1
5	0	0
5	0	0
6	1	1
4	-1	1
Mean = 5		Total = 4

Use the formula: s = √(4 / (6)) ≈ 0.82

Practice Questions

Calculate the sample standard deviation for the following data (round to 2 decimal places):

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