Evaluation of D2(N), D3(N), C4(N), and Related Statistics
The functions d2, d3, and c4 are used in the estimation of sigma from ranges or standard deviations. These functions are tabulated in practically all textbooks for quality control, for integer values of n. In Statistica, these functions are computed to a precision much higher than in published tables (i.e., usually with better than 12 digits of precision) and, hence, you may see small differences between the results computed by Statistica and those reported in published examples. Note that the results computed by Statistica are generally more precise. In addition, in practice, it is often necessary to evaluate these functions for non-integer (e.g., average) sample sizes. In Statistica, interpolated values will be computed for non-integer sample sizes.