Stably Updating Mean and Standard Deviation of Data By considering the (sample) mean of a set of data as a fit to this data by a constant function, a computational method is given based on a matrix formulation and Givens transformations. The (sample) mean and standard deviation can be updated as data accumulates. The procedure is numerically stable and does not require storage of the data. Methods for dealing with weighted data and data removal are presented. When updating the mean and square of the standard deviation, the process requires no square roots. CACM January, 1975 Hanson, R. J. mean, standard deviation, least squares, Givens transformation, updating estimates, removing data 5.5 5.19 CA750112 JB January 12, 1978 9:05 AM 2731 5 2799 2799 5 2799 2799 5 2799 2799 5 2799 3159 5 2799 3166 5 2799 3167 5 2799 1411 6 2799 2731 6 2799 2731 6 2799 2731 6 2799 2799 6 2799 2799 6 2799 2799 6 2799 2799 6 2799 3159 6 2799 3167 6 2799 3166 6 2799