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

International Tables for Crystallography (2006). Vol. F, ch. 11.5, p. 237   | 1 | 2 |

Section 11.5.3. Selection of reflections useful for scaling

C. G. van Beek,a R. Bolotovskya§ and M. G. Rossmanna*

aDepartment of Biological Sciences, Purdue University, West Lafayette, IN 47907-1392, USA
Correspondence e-mail:  mgr@indiana.bio.purdue.edu

11.5.3. Selection of reflections useful for scaling

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Both scaling methods 1[link] and 2[link] may take into account any reflection intensity observation, regardless of whether it is a partially or fully recorded reflection. However, there are significant differences between the selection of reflections in the two methods. Method 1[link] requires that all parts of a reflection are available in order to incorporate the reflection into the generalized HRS target, expression (11.5.2.3[link]). Thus, reflections that occur at the beginning or the end of the crystal orientation, or at gaps within the rotation range, must be rejected. Even when all parts of a reflection are recorded, there might be parts for which there was a problem during integration, thus making the reflection useless for scaling. The decision on whether all parts of a reflection are available for scaling is dependent on knowledge of the crystal mosaicity and of the crystal orientation matrix. Since these might be inaccurate, a reasonable tolerance has to be exercised when deciding if a reflection has been completely measured on consecutive frames. Method 2[link] allows the use of all reflections for scaling as every observation of a partial reflection is sufficient to estimate the intensity of a full reflection, expression (11.5.2.2[link]). However, a reasonable lower limit of calculated partiality has to be imposed in selecting reflections useful for scaling. The criteria for rejecting reflections prior to scaling and averaging are listed in Table 11.5.3.1[link].

Table 11.5.3.1| top | pdf |
Hierarchy of criteria for selecting reflections for scaling and averaging procedures

Methods 1 and 2
All parts of a reflection are rejected if:
(1) There are no successfully integrated parts.
(2) There are no parts with significant intensity (for scaling only).
(3) There are some parts entering and some parts exiting the Ewald sphere (this implies that the reflection is too close to the rotation axis and is partly in the blind zone).
(4) This is a full reflection recorded only once with no other symmetry-equivalent observations.
Method 1 Method 2
All parts of a reflection are rejected if: Any part of a reflection is rejected if:
(1) There is a part that is not successfully integrated. (1) The calculated partiality is less than a chosen value.
(2) There is a part that has a significant intensity, but is not predicted by the crystal orientation and mosaicity used in the scaling program. (2) The intensity is less than a chosen fraction of the error estimate.
(3) The sum of calculated partialities differs from unity by more than a chosen value.  








































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