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:The Welford algorithm as written calculates the sample variance in the finalize routine, and nowhere in the description does it specifically call that out. <!-- Template:Unsigned --><small class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:192.91.171.34|192.91.171.34]] ([[User talk:192.91.171.34#top|talk]] • [[Special:Contributions/192.91.171.34|contribs]]) </small>
===Parallel algorithm===
Is there an error in <math>M_{2,AB}</math>?
Chan et al. in its paper <ref name=":0">{{Citation
| last1 = Chan | first1 = Tony F. | author1-link = Tony F. Chan
| last2 = Golub | first2 = Gene H. | author2-link = Gene H. Golub
| last3 = LeVeque | first3 = Randall J.
| contribution = Updating Formulae and a Pairwise Algorithm for Computing Sample Variances.
| title = Technical Report STAN-CS-79-773
| publisher = Department of Computer Science, Stanford University
| year = 1979
| contribution-url =http://i.stanford.edu/pub/cstr/reports/cs/tr/79/773/CS-TR-79-773.pdf }}.</ref> has another relation for combining arbitrary sets <math>A</math> and <math>B</math>:
<math>M_{2,AB} = M_{2,A} + M_{2,B} + \frac{n_A}{n_B n_{AB}} \cdot \left( \frac{n_B}{n_A} \bar x_A - \bar x_B \right)^2 </math>, which yelds to <math>M_{2,AB} = M_{2,A} + M_{2,B} + \frac{1}{n_{AB}} \cdot \left( \bar x_A - \bar x_B \right)^2 </math> if <math>n_A</math> and <math>n_B</math> are equal.
=== Algorithm IV ===
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