has_metric_category single value ID based metric single run based metric ion source metric MS2 metric ratio of 4+ over 2+ of identified MS2 known precursor charges MS2 known precursor charges fractions Higher ratios of 3+/2+ MS2 precursor charge count may indicate e.g. preference for longer peptides in relation to identifiability. MS2-PrecZ-4 MS2-PrecZ-2 MS:4000172 MS IS-3C The ratio of 4+ over 2+ MS2 precursor charge count of identified spectra. The used type of identification should be noted in the metadata or analysis methods section of the recording file for the respective run. In case of multiple acceptance criteria (FDR) available in proteomics, PSM-level FDR should be used for better comparability.