Kendall's tau is a rank correlation, like Spearman's rho, that measures how consistently two variables are ordered. It handles small samples and many tied ranks well, which is why it is popular for agreement between two rankings or for short ordinal scales. Its values are typically smaller than Spearman's for the same data, so always say which coefficient you report.
What you need before you write a single word
- Which coefficient: τb (corrects for ties, the usual default) or τc.
- The coefficient and the sample size.
- The exact p value.
The APA 7 format template
A Kendall's tau-b correlation showed a [strong positive] relationship between [variable 1] and [variable 2], τb = .XX, p = .XXX, N = XX.
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Formatting rules reviewers actually check:
- Name the coefficient (τb or τc); τ is Greek, so it is not italicized.
- No leading zero on τ or p.
- Report N (some journals put it in parentheses after τ instead of df).
A worked example
Two judges each ranked the same 12 wines from best to worst. The rankings agreed closely, τb = .79, p < .001. Written up in APA 7:
A Kendall's tau-b correlation showed a strong positive relationship between the two judges' rankings of the 12 wines, τb = .79, p < .001.
Mistakes reviewers catch
- Calling it Spearman's rho or mixing the two. They are different coefficients on different scales.
- Not saying tau-b or tau-c. τb is standard for square tables and data with ties; τc for rectangular tables.
- Interpreting τ with Pearson benchmarks. τ values run lower than r for the same strength of relationship.
Let KyroStat do the write-up for you
KyroStat picks the rank correlation that fits your data and writes the sentence with the coefficient named.
Frequently asked questions
Kendall's tau or Spearman's rho? Both suit ordinal or non-normal data. Kendall's is preferred for small samples and many ties; Spearman's is more common and easier to compare with Pearson. See how to report a Spearman correlation.
Can I put Kendall's tau in a correlation table? Yes; say in the table note that the coefficients are Kendall's τb. See how to make an APA correlation table.
Is there a confidence interval? Some software gives one by bootstrapping; report it if you have it.