A priori estimates of the errors in experimental electron densities

A priori estimates of the suitability of a particular crystal for charge density analysis are discussed in terms of a simple criterion based on core electron concentration and a more detailed evaluation of the anticipated errors in the final deformation density maps. Predictions are compared with the results obtained in a series of studies and the implications for the design of a charge density analysis are discussed. It is found that counting statistics has often been a major contributor to the standard deviation of the charge density.