Unusual values — Data, 7–10
One result can be much bigger or smaller than the others. Spotting it matters because it can change a summary and may also tell us something important about what happened.
A result that stands apart
An unusual value is a result far from the rest of the data. In the numbers 4, 5, 5, 6 and 20, the 20 stands apart. It is not automatically wrong: it may be a real event, a different case or a recording mistake.
Why check unusual values?
A single unusual result can pull a mean up or down, so a summary may no longer describe most cases well. It can also be the most interesting result, such as a very long jump. Checking it helps us decide whether to keep it, correct a mistake or explain why it is different.
Check the 20
Five children score 4, 5, 5, 6 and 20 points. First, notice that 20 is far above the others. Next, check the record: if the child really scored 20, keep it and explain it; if 20 was meant to be 2, correct the data. Only then should we calculate a summary.
The trap: deleting the odd one
It is tempting to remove a value because it spoils a neat pattern. That seems fair when most results are close together. But unusual does not mean wrong: deleting a genuine result hides part of what happened. Check the original record before changing anything.
Where this helps
A nurse may notice a temperature much higher than a person's earlier readings and check it again. A coach may investigate a surprisingly fast time instead of ignoring it. In both cases, the unusual value might reveal an important change—or a measuring mistake.
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