unable to locate a method previously used for such interdisciplinary research synthesis.

As a result, we developed an approach to meet our charge. We gathered and evaluated research from a wide range of fields—from environmental and source monitoring and modeling to statistical methods, epidemiology, exposure assessment, toxicology, and clinical studies. We examined the quality of studies, judging them on the basis of the standards for the applicable academic discipline. For each topic, we examined the research from each contributing field and developed an overall judgment of the reduction in uncertainty that had occurred for that topic. We considered the state of understanding in 1997 and the amount of new information gained over the following 5 years. Our assessments of progress and scientific and policy value reflect our collective decisions about research progress for each topic (Appendix C).

The body of scientific evidence on PM and other air pollutants is only likely to grow in scope and complexity, and whether future decisions concern NAAQS or setting priorities for control strategies, they will demand enhanced tools and a protocol for assessing and synthesizing the evidence. Such techniques will benefit all decisionmaking agencies, as well as any successor to this committee (as recommended above) and other advisory committees. A standardized approach will make reviews of research programs more efficient, accessible, and comparable across institutions. More experience with methods such as this committee’s is likely to result in continual improvements in strategies for synthesizing and learning from the committee’s substantial investment in developing new answers to difficult questions.

The progress to date on meeting the committee’s research agenda is the result of sustained efforts by EPA, many other organizations, and the scientific community. The continuing needs for scientific research identified in Chapters 4 and 5 will require an even more intensive and well-managed program, both maintaining the momentum that has begun and addressing the underlying management challenges for EPA and other research agencies that have not been addressed to date.