Mapping principles: what a crosswalk cannot preserve

Mapped data is not the same data

Mapped data is not the same data. Crosswalks lose precision, and that matters for trends and for funding.

Precision differs

Crosswalks lose some information, because the precision of codes varies between revisions. Malignant neoplasm of breast is classified in ICD-10 by site only, and in ICD-11 by site and histopathology. So mapped data will not be exactly equivalent to what was first reported.

• 0 · 0 · partial
• 0 · 1 · partial

Track the condition

So be careful when interpreting data after a new revision begins. Analyses of temporal or regional trends, where several systems have been in use, should carefully track the condition under study.

• Caution · Interpretation · Be careful interpreting data collected after a new revision begins.
• The practice · Track · Analyses of trends where several systems were used should carefully track the condition under study.

Two years, and scrutiny

For grouping, WHO says countries should rely on code crosswalks for a suggested period of two years before refining their DRG classification. And for casemix, crosswalks need systematic review, with repeated scrutiny of backward maps against forward maps to ensure consistency at DRG level.

• Reliance · Two years · Countries transitioning should rely on code crosswalks for a suggested two years before refining their DRG classification.
• Review · Both ways · Crosswalks for casemix need repeated scrutiny of backward maps against forward maps, for consistency at DRG level.

Check yourself

Pause and think. How do ICD-10 and ICD-11 classify malignant neoplasm of breast? The answer: ICD-10 by site only; ICD-11 by site and histopathology. WHO's example: malignant neoplasm of breast is classified in ICD-10 by site only, and in ICD-11 by site and histopathology.

• ICD-10 by histopathology only; ICD-11 by site only
• Both by site only
• Both by site and histopathology
• ICD-10 by site only; ICD-11 by site and histopathology

Keep these in mind

Precision differs between revisions. Track the condition in trend analyses. And review forward and backward maps together for casemix.

• Precision differs between revisions
• Track the condition in trend analyses
• Review forward and backward maps together for casemix