From Statistics Explained
Comparability ratio in cause-of-death statistics is a measure, expressed as a ratio, indicating the net effect of a change in classification (e.g. from ICD-9 to ICD-10, or ICD-10 updates) or method (e.g. manual vs. automated coding) on a particular cause of death. Comparability ratios are the most usual way of presenting the results of a bridge coding study.