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 2003 Annual NRI, which
statistically updates 1997 NRI results with data collected during 2000 - 2003.
The NRI was conducted on a five-year cycle during the period 1982 to 1997, but
now is conducted annually. NRI data were collected every five years for 800,000
sample sites (8,397 sample sites in Illinois); annual NRI data collection occurs
at slightly less than 25 percent of these same sample sites.
NRI data release procedures are affected by implementation of an annual data
collection approach, because the scale of NRI estimates is affected by these
reduced sample sizes. Estimates are being released when they meet NRI
statistical standards and are scientifically credible in accordance with NRCS
policy, and in accordance with OMB and USDA Quality of Information Guidelines.
The 2003 Annual NRI data are suitable for national, many regional, and some
state level analyses. Selected state-level results are reported here. These
results will be supplemented in early to mid 2008 with additional estimates that
compare net change and land cover/use dynamics with previous inventories.
Until these supplements are released, direct comparisons between 1997 and 2003
NRI estimates to determine change or trends will produce incorrect inferences
and is scientifically invalid.