Statistical symbols and abbreviations — a lookup table
What every statistical letter and Greek symbol stands for, the sample-vs-population pairs that cause the most confusion, and how APA style wants each one typeset.
The core convention: Latin letters describe your SAMPLE; Greek letters describe the POPULATION they estimate.
| Sample (Latin) | Population (Greek) | Quantity |
|---|---|---|
| M or x̄ | μ (mu) | Mean |
| s or SD | σ (sigma) | Standard deviation |
| s² | σ² | Variance |
| r | ρ (rho) | Correlation |
| p̂ or p | π (pi) | Proportion |
| b | β (beta) | Regression coefficient |
| n (subgroup) / N (total) | N | Sample / population size |
| Symbol | Name | Meaning / where you meet it |
|---|---|---|
| p | p-value | Probability of a result at least this extreme if H0 is true. Italic, no leading zero: p = .03. |
| α (alpha) | Significance level | The false-positive rate you accept in advance, usually .05. (Same letter, different meaning: Cronbach’s α.) |
| β (beta) | Type II error rate | Probability of missing a true effect; power = 1 − β. (Also: standardized regression coefficient.) |
| t | Student’s t | t-tests and regression coefficients; reported with df: t(24) = 2.31. |
| F | F statistic | ANOVA and overall regression tests; two dfs: F(2, 57) = 4.40. |
| χ² | Chi-square | Categorical association and goodness of fit: χ²(1, N = 120) = 5.24. |
| z | Standard normal deviate | Large-sample and proportion tests; also standardized scores. |
| U | Mann–Whitney U | Nonparametric two-group comparison. |
| W | Wilcoxon / Shapiro–Wilk | Signed-rank statistic; also the normality test statistic. |
| df | Degrees of freedom | Independent information behind an estimate; determines the reference distribution. |
| CI | Confidence interval | Range of parameter values compatible with the data: 95% CI [0.21, 1.03]. |
| SE / SEM | Standard error (of the mean) | SD of a statistic’s sampling distribution: SE = SD/√n. |
| H0 / H1 (Ha) | Null / alternative hypothesis | The "no effect" default and its rival. |
| λ (lambda) | Wilks’ lambda | MANOVA test statistic (also: Poisson rate parameter). |
| ε (epsilon) | Sphericity correction / error | Greenhouse–Geisser ε in repeated measures; residual error term in models. |
| Symbol | Name | Meaning |
|---|---|---|
| d | Cohen’s d | Standardized mean difference (benchmarks .2/.5/.8). |
| g | Hedges’ g | Small-sample-corrected d. |
| r | Pearson correlation | Linear association, −1 to +1; r² = shared variance. |
| ρ / rs | Spearman correlation | Rank-based (monotonic) association. |
| R² | Coefficient of determination | Variance explained by a regression model; adjusted R² penalizes predictors. |
| η² / η²p | (Partial) eta squared | ANOVA variance explained; the partial version is not comparable across designs. |
| ω² | Omega squared | Less-biased alternative to η². |
| f | Cohen’s f | ANOVA effect size used by power software (G*Power). |
| V | Cramér’s V | Effect size for contingency tables, 0–1. |
| φ (phi) | Phi coefficient | Correlation for 2 × 2 tables. |
| OR / RR | Odds ratio / risk ratio | Binary-outcome effect sizes; OR > RR when the outcome is common. |
| κ (kappa) | Cohen’s kappa | Chance-corrected inter-rater agreement. |
| α | Cronbach’s alpha | Internal consistency of a scale (≥ .70 conventional floor). |
| ICC | Intraclass correlation | Reliability of continuous ratings; also clustering in multilevel models. |
| Δ (delta) | Change / difference | ΔR² = increment in variance explained between nested models. |
Typesetting rules (APA 7)
Italicize Latin-letter statistical symbols: N, n, M, SD, df, t, F, p, r, d, R². Do NOT italicize Greek letters (α, β, χ², η²) or ordinary abbreviations (CI, ANOVA, HR). Subscripts that are labels stay roman: in "M_control", the M is italic and "control" is not.
Numbers: statistics that cannot exceed 1 (p, r, η², α as reliability) drop the leading zero (p = .04, r = .31); those that can exceed 1 keep it (d = 0.50, t = 2.31). Report exact p-values to two or three decimals, with p < .001 as the floor.
Spacing: put spaces around = and < (t(24) = 2.31, p < .001), report df in parentheses immediately after the statistic letter, and give χ² its sample size: χ²(1, N = 120) = 5.24.
Frequently asked questions
What is the difference between M and μ (and s and σ)?
Why does α mean two different things?
How do I type these symbols?
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