Statistics and reports on environmental damage and progress routinely come from dozens — if not hundreds — of nonprofit, government, and other agencies. Often the information disagrees with previously published data, creating difficulty in assessing the health of the nation’s environment. A report, “The State of the Nation’s Ecosystems,” released Sept. 24, 2002, was an effort by 150 experts in business, government, environmental organizations, and academia to make sense of the picture. The 270-page document makes the argument that just as economic policies in the United States are set after the examination of key economic data, environmental policy ought to be based on similar broadly accepted indicators. “There’s lots of data,” said William Clark, chairman of the project and Harvey Brooks Professor of International Science, Public Policy and Human Development at Harvard’s Kennedy School of Government. “The analogy we’re using is that we’re [currently] doing environmental policy for the nation in a way that’s equal to doing economic policy with just companies’ annual reports and reports from chambers of commerce.” If it’s successful, Clark said, the report will shift environmental disputes from arguments over the accuracy or appropriateness of particular data to policy debates based on mutually agreed-on data.