populations, limiting national representativeness and not allowing inferences about the national population.

Another data source that will have to be seriously considered depending on the indicator sets suggested, is the collection of new survey data that contains desired information and is referent to the American population and select population groups. There may be incumbent costs, the magnitude of which will depend on the extent of the survey, but these can be constrained by “piggy-backing” relevant survey items on existing surveys that are being conducted on an ongoing basis. Some candidate surveys may not be devoted centrally to health issues, but may be exploring labor, economic or other themes.

Physiological Measures

Theoretically, it might be of great interest to have leading indicators represented by physiological or biochemical measures. Examples might include blood pressure levels, blood levels of antibodies representing exposure to designated infectious diseases, blood levels of important nutrients such as vitamins, or population-average muscle strength or physical balance capacity as a reflection of physical dysfunction. Many, if not all of these, might be available on a national sample survey such as the NHANES. However, there are formidable impediments to these measures, the most prominent of which is cost. Such routine data collection would be extremely expensive. In addition, such data may not be available in a timely manner or for select population groups. The NHANES is only performed once each decade, and would not be suitable to inform policy on a regular basis; there are no other equivalent surveys of national scope. Finally, the processing of physiological and other laboratory data might add incremental delays in making the data available on a real time basis.

Timeliness of Data and Indicator Availability

In addition to timeliness of physiological information, there is an issue relevant to more conventional data sources. Provision of “final” vital records data may take up to 3 or 4 years after the year in which they were collected. Consequently, measures of leading indicators based on vital records, such as mortality or birth-related information, would have to be based on provisional information and subject to change at a later date. Even routinely collected national survey data may be subject to delays of 6 months to 2 years while the data are validated, analyzed, and presented for appropriate use. This will have relevance to the frequency and recency of reporting to the population on the status of specific indicators.

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