One embodiment of the invention provides a method for determining the standard deviation of a data sample. The method considers the distribution of the data in the context of cumulative probability. The empirical probability of a plurality of values is determined. The quantiles of the normal distribution for each empirical probability is then obtained. A robust linear regression of the quantiles versus the plurality of values is performed. Then the slope of the robust linear regression is determined and the inverse of the slope serves as an estimate of the standard deviation.