Open AccessScaling and assessment of data quality
Author(s) -
Evans Philip
Publication year - 2006
Publication title -
acta crystallographica section d
Language(s) - English
Resource type - Journals
ISSN - 1399-0047
DOI - 10.1107/s0907444905036693
Subject(s) - scaling , symmetry (geometry) , data set , diffraction , set (abstract data type) , point (geometry) , quality (philosophy) , scale (ratio) , homogeneous space , correlation , resolution (logic) , statistical physics , computer science , statistics , mathematics , data mining , physics , optics , artificial intelligence , geometry , quantum mechanics , programming language
The various physical factors affecting measured diffraction intensities are discussed, as are the scaling models which may be used to put the data on a consistent scale. After scaling, the intensities can be analysed to set the real resolution of the data set, to detect bad regions ( e.g. bad images), to analyse radiation damage and to assess the overall quality of the data set. The significance of any anomalous signal may be assessed by probability and correlation analysis. The algorithms used by the CCP 4 scaling program SCALA are described. A requirement for the scaling and merging of intensities is knowledge of the Laue group and point‐group symmetries: the possible symmetry of the diffraction pattern may be determined from scores such as correlation coefficients between observations which might be symmetry‐related. These scoring functions are implemented in a new program POINTLESS .