I/σI {Rmerg, Rmeas, Rpim, CC1/2} for Crystal Diffraction Data Quality Evaluation.

X-ray crystal diffraction has provided atomic-level structural information on biological macromolecules. Data quality determines the reliability of structural models. In most cases, multiple data sets are available from different crystals and/or collected with different experimental settings. Reliable metrics are critical to rank and select the data set with the highest quality. Many measures have been created or modified for data quality evaluation. However, some are duplicate in functionality, and some are likely misused due to misunderstanding, which causes confusion or problems, especially at synchrotron beamlines where experiments proceed quickly. In this work, the capability, significance, effectiveness, and correlations of these measures are studied through both theoretical analysis and experimental data to clarify confusion and misuses, and thus identify the most reliable measures for evaluating data quality from different aspects.