Standard deviation
Also called: SD · Topic: Geographical Data: Sources, Compilation and Processing · NCERT: Class 12, Ch 4 "Spatial Information Technology"
Meaning
Standard deviation (SD) is the most widely used measure of dispersion, which means how spread out values are. Find how far each value lies from the mean and square each distance. Take the average of the squares, then take the positive square root. A bigger SD means the values are more scattered. Squaring removes the minus signs and gives extra weight to values far from the mean. SD is also the base of the coefficient of variation (SD ÷ mean × 100).
Example
Rainfall in Barmer in western Rajasthan swings widely from year to year. Its yearly totals would give a large SD compared with its low mean. This is why the coefficient of variation of rainfall there is above 50%, while it is below 25% on the west coast.
Don't confuse with
- Mean deviation: it simply ignores plus and minus signs. SD squares the distances and then takes the square root.
- Coefficient of variation: it is SD as a percentage of the mean. Use it to compare data sets with different averages.
Related concepts
- Measures of dispersion
- Range
- Mean deviation
- Coefficient of variation
- Measures of relationship
- Correlation coefficient