NNDSS data might provide a gross measure of a state's changing rate of a reported disease, but not be appropriate (except for a few diseases) for comparing small changes in rates of incidence.

The lack of appropriate data may be the most important factor limiting effective monitoring of public health performance. States and the federal government may need to use data collected for other purposes and to rely on data that are not entirely comparable across states. Understanding the limits of such data is important if performance monitoring is to be effective.

One use of public health performance measures might be to examine and compare the effects of public health interventions among states. In that case, individual states and the federal government will want to compare the outcomes of similar (and different) interventions in different settings. For this purpose, comparable health outcomes data are needed from all states. However, states have had little incentive to standardize their data collection efforts with those of other states. A notable exception has been the development of the vital statistics system, a cooperative state-federal administrative data system that contains considerable health information. Data collection efforts at the national level (sponsored by the federal government or organizations with national and multistate agendas) are usually in a better position to collect health-related data using comparable definitions, questions, and methods across many or all states. Others, such as the Behavioral Risk Factor Surveillance System (BRFSS) and the Healthcare Cost and Utilization Project, use similar questions and definitions but differ in methods. Largely because of budget constraints, however, national data collection efforts such as the National Health Interview Survey (NHIS) usually have as their objective the provision of national population estimates of health, and they have not yet had the sample size or sample design required to make state-level estimates.

Two surveys designed to generate state-level estimates are the National Immunization Survey (NIS) and the BRFSS. The NIS is a random-digit-dial telephone survey of households with small children, using samples drawn from all 50 states, Washington, D.C., and 27 metropolitan areas. The survey yields state and regional estimates of immunization completeness for children aged 19–35 months. This federally run survey uses comparable data collection methods across all states and regions, and comparisons of rates of immunization can reasonably be made among states.

BRFSS is a state survey designed to assess the prevalence of health-related behavioral risk factors associated with the leading causes of premature death and disability. It is a random-digit-dial survey of samples that can be generalized to state populations. While the CDC provides overall support and technical oversight for the BRFSS, individual states administer the survey and have the opportunity to add their own questions. As a result, sampling design and data collection methods may vary from state to state. Consequently, BRFSS data should be used cautiously when making comparisons among states. For example, if states



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