Statistical Skills: Mean, Median, Mode & Quartiles

Statistical techniques allow geographers to summarise data, identify patterns and test whether results are significant. At GCSE you need to be able to calculate and interpret a range of statistical measures. This lesson covers all the statistical skills required for AQA GCSE Geography.

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Measures of Central Tendency

Central tendency measures tell you the typical or average value in a dataset.

Mean

The mean is the sum of all values divided by the number of values.

Formula: Mean = Σx / n

where Σx = sum of all values and n = number of values

Example: River pebble sizes (mm): 12, 15, 18, 22, 25, 30, 35

Mean = (12 + 15 + 18 + 22 + 25 + 30 + 35) / 7 = 157 / 7 = 22.4 mm

Advantages: Uses all the data; widely understood.

Disadvantages: Can be distorted by extreme values (outliers).

Median

The median is the middle value when the data is arranged in order from smallest to largest.