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Wetlands - About the Data

Estimates presented here are based upon the latest information from the National Resources Inventory (NRI). The NRI is a longitudinal sample survey based upon scientific statistical principles and procedures. It is conducted by the U.S. Department of Agriculture’s Natural Resources Conservation Service (NRCS), in cooperation with Iowa State University’s Center for Survey Statistics and Methodology.

These results are based upon the 2007 NRI, which provides nationally consistent data for the 25-year period 1982–2007. The estimates in this wetlands report cover the conterminous 48 States only. Separate estimates also cover Hawaii, Alaska, and the Caribbean Area.

Release of NRI results is guided by NRCS policy and is in accordance with OMB and USDA Quality of Information Guidelines developed in 2001. NRCS is releasing NRI estimates only when they meet statistical standards and are scientifically credible in accordance with these policies; also, measures of statistical uncertainty are provided for all 2007 NRI estimates released to the public.

The NRI approach to conducting inventories facilitates examination of trends in wetlands over time because –

  • the same sample sites have been studied since 1992
  • the same data have been collected since 1992 [definitions and protocols have remained the same]
  • quality assurance and statistical procedures ensure that trend data are scientifically legitimate and unambiguous.

NRI classification of wetlands is slightly different than that used by the Fish & Wildlife Service (FWS) in their statistically based Wetlands Status and Trends study. The NRI and the FWS inventory have different legislative mandates, sampling methodology, data collection processes, estimation procedures, and analysis routines that evolved independently over the past two decades, even though both survey programs use the Cowardin classification system. Recent collaborative efforts have resulted in enhanced classifications for both programs, but wetlands data collected by the two agencies are currently not comparable. The NRI multi-resource approach is beneficial to USDA analysts and others who examine conservation and agri-environmental issues.

Irrespective of the scale of analysis, margins of error must be considered. Margins of error (at the 95 percent confidence level) are presented for all NRI estimates. Note that estimates of change between two points in time will be less precise (relatively) than estimates for a single inventory year because the changes will be occurring on a smaller fraction of the landscape.


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