By using comparable instruments, it is possible to track the changes in preparedness levels across time. Similarly, it is possible to compare injury rates or other health impacts across time, place, and disaster type. In addition, risk factors can be identified for health outcomes. For example, in the Northridge earthquake, those over age 60 years were three times more likely to be hospitalized or die as a result of injuries than were those aged 20-59 years. Interventions can be evaluated.
Surveys are useful tools for identifying and evaluating the health impacts of disasters.