title: Robust background modelling inDIALS.
abstract: A method for estimating the background under each reflection during integration that is robust in the presence of pixel outliers is presented. The method uses a generalized linear model approach that is more appropriate for use with Poisson distributed data than traditional approaches to pixel outlier handling in integration programs. The algorithm is most applicable to data with a very low background level where assumptions of a normal distribution are no longer valid as an approximation to the Poisson distribution. It is shown that traditional methods can result in the systematic underestimation of background values. This then results in the reflection intensities being overestimated and gives rise to a change in the overall distribution of reflection intensities in a dataset such that too few weak reflections appear to be recorded. Statistical tests performed during data reduction may mistakenly attribute this to merohedral twinning in the crystal. Application of the robust generalized linear model algorithm is shown to correct for this bias.
authors.affiliation: Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK; Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: James M
authors.initials: JM
authors.lastname: Parkhurst
authors.affiliation: Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK.
authors.forename: Graeme
authors.initials: G
authors.lastname: Winter
authors.affiliation: STFC Rutherford Appleton Laboratory, Didcot OX11 0FA, UK; CCP4, Research Complex at Harwell, Rutherford Appleton Laboratory, Didcot OX11 0FA, UK.
authors.forename: David G
authors.initials: DG
authors.lastname: Waterman
authors.affiliation: Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK.
authors.forename: Luis
authors.initials: L
authors.lastname: Fuentes-Montero
authors.affiliation: Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Gildea
authors.affiliation: Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK.
authors.forename: Garib N
authors.initials: GN
authors.lastname: Murshudov
authors.affiliation: Diamond Light Source Ltd, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK.
authors.forename: Gwyndaf
authors.initials: G
authors.lastname: Evans
keywords: background modelling; generalized linear models; integration; robust outlier rejection