1) D. E. Knuth (1998). The Art of Computer Programming (Volume 2): Seminumerical Algorithms. Third Edition. Page 232.
2) B. P. Welford (1962). Note on a Method for Calculating Corrected Sums of Squares and Products. Technometrics (Volume 4, Number 3). Pages 419-420.
Link: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.302.7503
3) T. F. Chan, G. H. Golub, and R. J. LeVeque (1983). Algorithms for Computing the Sample Variance: Analysis and Recommendations. The American Statistician (Volume 37, Number 3). Pages 242-247.

This is also derived from the following:

1) D. E. Knuth (1998). The Art of Computer Programming (Volume 2): Seminumerical Algorithms. Third Edition. Page 232.

2) B. P. Welford (1962). Note on a Method for Calculating Corrected Sums of Squares and Products. Technometrics (Volume 4, Number 3). Pages 419-420.

Link: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.302.7503

3) T. F. Chan, G. H. Golub, and R. J. LeVeque (1983). Algorithms for Computing the Sample Variance: Analysis and Recommendations. The American Statistician (Volume 37, Number 3). Pages 242-247.