For agricultural statistics in general, and for the EU and the NASS survey programmes in particular, the coverage (for the different crops such as acres of corn or the number of cattle represented by the farms on the frame) is a very important issue. In the regulations used for EU statistics, the desired accuracy and coverage are described in detail. Furthermore, countries are requested to provide detailed metadata and quality information.
In general, active records eligible for survey samples account for 80-95% of total US production for most major items. Medium to large size operations are typically sampled at higher rates as they represent a greater proportion of production being measured. This is adequate for the survey programme where the major focus is agricultural totals at the federal and state levels. For the census programme, the focus is county-level data on farm numbers by type and size, demographics, acreage, production, inventory, sales, labour, and other agricultural census items. Consequently, adequate coverage of all types and sizes of farms is needed to ensure reliable census results.
Even though the NASS publishes coverage-adjusted census data, a specific issue for the USA is the need for adequate list frame coverage for all types and sizes of farms to ensure reliable county-level data for all census items. Although coverage goals are established to generate increased agency attention to list-building needs, coverage of the total number of farms has been decreasing over the last few censuses. These decreases are due primarily to the increasing number of small farms which are difficult to locate through traditional list-building approaches. Also, they are difficult to properly maintain on the list frame due to their borderline 'farming/not farming' status. Small farms routinely enter and exit at a faster pace than larger, more commercial size farms. To keep coverage high for farm numbers, the NASS must keep rebuilding its lists. Additionally, before conducting the 2007 Census of Agriculture, the NASS recognized the extensive interest in minority farm numbers and specialty commodity farms and attempted to improve the reliability of these data through extensive list-building efforts.
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