A simple test based on Bayesian statistics for the presence of minority populations in single‐crystal structure refinement is presented. The test is illustrated by analysis of photocrystallographic experiments on single crystals of ruthenium–sulfur‐dioxide‐based
complexes. In data sets collected after irradiation with light, conventional refinements of the populations of different metastable states to values below 4% are shown to be statistically significant. The results also confirm that the photo‐induced states are absent from data collected
in the dark.