Mean deviation
Topic: Geographical Data: Sources, Compilation and Processing · NCERT: Class 12, Ch 4 "Spatial Information Technology"
Meaning
Mean deviation is a measure of dispersion, which means it tells you how spread out values are. To find it, measure how far each value lies from a central value, usually the mean or the median. Drop the plus and minus signs, so every distance counts as positive. Then take the average of these distances. A small mean deviation means the values stay close to the centre. A large one means they are scattered.
Example
The normal rainfall of seven districts on the Malwa plateau in Madhya Pradesh averages 926.29 mm. Dewas gets 1,083 mm, so it lies 156.71 mm above the mean. Mandsaur gets 825 mm, so it lies 101.29 mm below, which counts as 101.29. Average these distances for all seven districts and you get the mean deviation.
Don't confuse with
- Standard deviation: it squares each distance before averaging and then takes the square root. Mean deviation simply ignores the signs.
Related concepts
- Measures of dispersion
- Range
- Standard deviation
- Coefficient of variation
- Measures of relationship
- Correlation coefficient