Cryst. Rev. (2010), 16(2), 133-144. [ doi:10.1080/08893110903483238 ]
Recent developments in crystallographic error analysis are described. This report provides an introduction to more-formal work, originally published in Ref. (Haestier, J., J. Appl. Cryst. 2009, 42, 798). Prior to the main discussion, a brief overview of the normal distribution and error-propagation is provided, with some simplified examples to demonstrate the effects of covariance terms on error calculations. A new method is described for absorbing the cell-parameter errors into the variance-covariance matrix of the refined parameters. Problems occur for monoclinic and triclinic cell settings as the crystallographer must ‘choose’ how errors on the cell angles affect the coordinates. The choice has no effect on error-calculations on the internal geometry (bond-lengths, angles and torsion angles) of the structure, but may introduce a bias if the errors are used as weights.