Measures of Central Tendency
These are single values that represent an entire data set.
Mean (Average)
Mean = Sum of all values ÷ Number of values
Data: 12, 15, 18, 20, 25
Mean = (12+15+18+20+25) ÷ 5 = 90 ÷ 5 = 18
Median (Middle value)
Arrange data in order, then find the middle value.
Data: 3, 7, 9, 12, 15 → Median = 9 (middle value)
Even number: Data: 4, 6, 10, 14 → Median = (6+10)÷2 = 8
Mode (Most frequent)
The value that appears most often.
Data: 2, 3, 3, 5, 7, 3, 8 → Mode = 3 (appears 3 times)
Range
Range = Highest value − Lowest value
Data: 4, 9, 15, 21, 30 → Range = 30 − 4 = 26
Frequency Distribution Tables
Organise data into classes. Calculate the mean using:
Mean = Σ(fx) ÷ Σf where f = frequency and x = class midpoint.
When to Use Which Measure
- Mean: best for symmetrical data with no extreme outliers
- Median: best when there are extreme values (e.g. income data)
- Mode: best for categorical data (most popular colour, shoe size)