Tables for
Volume F
Crystallography of biological macromolecules
Edited by E. Arnold, D. M. Himmel and M. G. Rossmann

International Tables for Crystallography (2012). Vol. F, ch. 11.4, p. 291   | 1 | 2 |

Section Estimation of multiplicative errors

Z. Otwinowski,a* W. Minor,b D. Boreka and M. Cymborowskib

aUT Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75390–9038, USA, and bDepartment of Molecular Physiology and Biological Physics, University of Virginia, 1300 Jefferson Park Avenue, Charlottesville, VA 22908, USA
Correspondence e-mail: Estimation of multiplicative errors

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The multiplicative scale factor has its own uncertainty independent of random errors with typical values in the range of a few per cent. However, even such small errors are important in calculations of the phase signal. Errors in the scale factors have a correlated component that equally affects measurements of intensities in phasing differences, so it does not impact on the differences themselves. The important part is estimating the magnitude of the remaining component of scaling errors, described by σK. Comparing symmetry-related reflections estimates only the relevant component of multiplicative errors. The total scaling error would have to be estimated differently, but typically it has little relevance to macromolecular crystallography and can be ignored.

The σI [equation ([link]] can be combined with σK to obtain the final estimated error of the scaled measurement:[\sigma_E=(1/K)(\sigma_I^2+I^2\sigma_K^2)^{1/2}.\eqno(]

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