| 1. Level 1 (very high)—codes with serious policy implications. These are causes for which the true UCOD could belong to more than one broad cause group, for example, septicaemia. Such errors can potentially grossly misinform understanding of the extent of an epidemiological transition in a population.|
2. Level 2 (high)—codes with substantial implications. These are causes for which the true UCOD is likely to belong to only one or two of the three broad groups (i.e. ‘essential (primary) hypertension’). While not altering the understanding of the broad composition of mortality in a population, these codes can significantly affect the comparative importance of leading causes within broad disease categories.
3. Level 3 (medium)—codes with important implications. These are causes for which the true underlying UCOD is likely to be within the same ICD chapter. For instance, ‘unspecified cancer’ still identifies the death as being due to cancer and thus has some policy value, although greater type (site) specificity is required as different strategies are applied for different sites of cancer (i.e. breast versus lung).
4. Level 4 (low)—codes with limited implications. These are diagnoses for which the true UCOD is likely to be confined to a single disease or injury category (e.g. unspecified stroke would still be assigned as a stroke death). The implications of unusable causes classified at this level will therefore generally be much less important for public policy.