mean, median concept
| Definition | The mean of a sample is its average and the median its middle value once sorted. One wild value moves the mean and leaves the median, which is why the book reports a median where one value can be wild. Primer S, equation S.9. Also sample mean. |
|---|---|
| Example | 2, 4, 4, 4, 5, 5, 7, 9 has mean 5 and median 4.5, and with the 9 changed to 90 the mean is 15.125 while the median stays 4.5. |
| Book | Data Mining as Observation, draft 0.2, commit f3914f0; entry id mean-median, kind concept. |
| Status | no ledger row names this entry. Corrections: none recorded. |
| Defining equation | Book equation S.9. |
| Assumptions and scope | none |
| Prior art | none recorded |
| Evidence | none |
| Reviewed | semantic review 2026-09-09; generated 2026-09-10 from records at the commits on the provenance page. |
Equation
Book equation S.9.
\[\bar x=\frac1n\sum_i x_i,\qquad s^{2}=\frac{1}{n-1}\sum_i(x_i-\bar x)^{2}.\]
Conditions
none
Ledger
none
First stated
Primer S section S.4 of Data Mining as Observation, added in draft 0.3 (2026-09-09) for the ECE 514 readers whose first courses are far behind. The idea is standard and TSK Appendix C covers it at length.
Measurements
none
Failures and corrections
none
Invariance envelope
none declared
Machine checked
none
Used in
Data Mining as Observation primer S, chapters 2, 4, 6, 7, 11, 13.
Related
expectation; percentile; standard deviation; skewness.
See also
none
Status
Generated 2026-09-10 by encyclopedia/generate.py; book
at observation-data-mining f3914f0; the commit of every record is listed
in the encyclopedia’s provenance.