Why this is mistaken
The sample mean is known for the selected rows; the population mean is fixed but usually unknown. Use the statistic as an estimate only under a stated design and preserve the distinction in notation and prose.
Where to watch
When this mistake may appear
- Only one sample is visible.
- A point estimate is reported without uncertainty or notation.
Check your work
Your work may contain this mistake if:
- Calls 31.875 the mean of all 480 invoices.
- Uses x-bar and mu as synonyms.