In which fields are citations indicators of research quality?

Citation counts are widely used as indicators of research quality to support or replace human peer review and for lists of top cited papers, researchers, and institutions. Nevertheless, the extent to which citation counts reflect research quality is not well understood. We report the largest-scale evaluation of the relationship between research quality and citation counts, correlating them for 87,739 journal articles in 34 field-based Units of Assessment (UoAs) from the UK. We show that the two correlate positively in all academic fields examined, from very weak (0.1) to strong (0.5). The highest correlations are in health, life sciences and physical sciences and the lowest are in the arts and humanities. The patterns are similar for the field classification schemes of Scopus and Dimensions.ai. We also show that there is no citation threshold in any field beyond which all articles are excellent quality, so lists of top cited articles are not definitive collections of excellence. Moreover, log transformed citation counts have a close to linear relationship with UK research quality ranked scores that is shallow in some fields but steep in others. In conclusion, whilst appropriately field normalised citations associate positively with research quality in all fields, they never perfectly reflect it, even at very high values.