The Hurst exponent is estimated by fitting the power law formula_20 to the data. This can be done by plotting formula_21 as a function of formula_22, and fitting a straight line; the slope of the line gives formula_23 (a more principled approach fits the power law in a maximum-likelihood fashion). Such a graph is called a box plot. However, this approach is known to produce biased estimates of the power-law exponent. For small formula_3 there is a significant deviation from the 0.5 slope. Anis and Lloyd estimated the theoretical (i.e., for white noise) values of the R/S statistic to be: