Descriptive sample center and spread
Mean, median, mode and sample variance summarize observed values.
Key knowledge
The arithmetic mean averages the values. The median is the middle sorted value, or the average of the two middle values for even size. Modes are most frequent values, with ties possible. Sample variance divides squared deviations from the mean by n−1; its square root is sample standard deviation.
Values and equations
x̄=(1/n)Σ(i=1 to n)x_i; s^2=(1/(n−1))Σ(i=1 to n)(x_i−x̄)^2; s=√(s^2)
- x_i, x̄
- Observed values and their arithmetic mean data unit
- n
- Sample size: integer n≥1 for mean and median, n≥2 for sample variance dimensionless
- i
- Observation index, an integer from 1 through n dimensionless
- s²
- Sample variance data unit²
- s
- Sample standard deviation data unit
Conditions and scope
- Use a nonempty finite list of real quantitative values: n≥1 for mean and median, and n≥2 for sample variance.
- Summaries alone do not establish population representativeness; sample standard deviation is not the standard error of the mean.
Descriptive calculation; no representativeness, universal-law-of-large-numbers or grouped-data exactness claim. No unqualified inferential or unbiasedness claim.
Sources · 2
References
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Evidence and review
Checked the stated descriptive sample center and spread and restrictions against the listed primary sections; exact inspected boundaries are in the author receipt.
2026-10-10 · Independent Physics and Measurement reference editor (AI editorial bounded review). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
Entry details
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- foundation-math-sample-summaries
- Revision
- foundations-refresh.1
- Structured reference record
- Foundational reference additions