Mean
Also called: Arithmetic mean, Average · Topic: Geographical Data: Sources, Compilation and Processing · NCERT: Class 12, Ch 2 "Data Processing"
Meaning
The mean, or arithmetic mean, is the sum of all values divided by the number of values. For grouped data, each class midpoint (the middle value of the class) is multiplied by its frequency. These products are added and divided by N, so mean = Σfx ÷ N. The mean uses every value, but very large or very small values pull it towards them. This is why an average can sometimes mislead.
Example
The normal rainfall of seven Malwa plateau districts in Madhya Pradesh adds up to 6,484 mm, so the mean is 6,484 ÷ 7 = 926.29 mm. In NCERT's warning, river depths of 0.6, 0.8, 0.9 and 1.5 m give a mean of 0.95 m. A 1 m tall child still drowned in the deep part.
Don't confuse with
- Median: the middle value by position, so extreme values do not affect it.