Definition
Random variation
Chance-made differences between results from repeated samples, measurements, or trials.
What it means
Repeat the same chance process and the results need not be identical. Which outcomes happen, or which members enter a sample, changes by chance. Those ups and downs are random variation; they do not automatically mean that the rule or population changed.
Remember it
Same setup, slightly different results: chance can wiggle the numbers.
Example
Five groups each toss a fair coin 20 times. They get 8, 9, 10, 11, and 13 heads. The changing head counts are random variation from the tosses.
Watch for
If a spinner is bent so one colour is more likely, the repeated difference is a systematic bias, not merely random variation.
Common mix-up
Larger samples often reduce the size of sampling variation compared with the total, but they do not remove chance completely.
Exact meaning
Random variation is the unpredictable difference in outcomes or estimates caused by chance when the same random process, sampling method, or measurement situation is repeated.