While mortality data can serve as proxies for morbidity information about a population, morbidity data are more helpful in clarifying the reasons for particular trends in mortality. Also, changes in death rates could be due to changes in morbidity rates or in case-fatality.

Trends in morality data may be artifactual:

1. Reflecting changes in coding practices (ICD revisions, training of physicians);
2. Diagnostic capabilities (new tests, procedures for assigning diagnosis);
3. Denominator population (changing geographic coverage or census inaccuracies).