How are comparability ratios applied?
The comparability ratio is multiplied by counts or rates calculated for time periods that are classified by ICD-9. For example, there were 1,717 deaths due to pneumonia and influenza (ICD-9 480-487) to residents of Washington residents in 1998. Applying the comparability ratio of 0.70 to the 1998 number of deaths (1,717) will give the adjusted number of 1,202 deaths due to pneumonia and influenza. This modified count can be compared to the 1,258 deaths due to pneumonia and influenza (ICD-10 J10-J18) that occurred in 1999. Thus, after adjusting for the effects of the ICD revision change, there was only an increase of 56 deaths in 1999 (instead of a large decrease when comparing unadjusted counts). For a guide on how to present ICD-10 Mortality Data go to: http://www.doh.wa.gov/ehsphl/chs/chs-data/death/icd10/ICD10Gud.
