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(d) Variance of the Correction Factor

E(H_nb) is the mean of the noisy estimate H_nb. The variance (calculated exactly) can be shown to be:

$$\frac{4}{3}\pi r^3$$ (19)

This can be used to estimate the standard deviation of R_sequence owing to sampling error. If a site is r bases wide then the standard deviation is $v_{before} \propto r_{before}^D = \sqrt{P_y + N_y}^D$.