Table 1

Environmental variables used to predict AIV in wild birds in the US.

Variable

Source

Manipulation


Binary variable: 1 if the county ever froze, 0 otherwise

ftp://sidads.colorado.edu/pub/DATASETS/NOAA/G02156/metadata/ webcite

Calculated from freeze and thaw date

Freeze date

ftp://sidads.colorado.edu/pub/DATASETS/NOAA/G02156/metadata/ webcite

Calculated as the first day of the year when more than half of the county was frozen

Harvested cropland (ha)

http://www.nationalatlas.gov/atlasftp.html webcite

None

Human population density

http://www.nationalatlas.gov/atlasftp.html webcite

The total human population was divided by the area of the county

Mean farm size (ha)

http://www.nationalatlas.gov/atlasftp.html webcite

None

Minimum temperature (°C)

http://www.prism.oregonstate.edu/products/matrix.phtml?year0=2000 webcite

Calculated as the average minimum temperature of all of the 800 m pixels in the county

Percent family owned farms

http://www.nationalatlas.gov/atlasftp.html webcite

None

Percent of county in cropland

http://www.nationalatlas.gov/atlasftp.html webcite

None

Poultry density

http://www.fao.org/geonetwork/srv/en/resources.get?id=12720&fname=glbpo25cor.zip&access=private webcite

The data were aggregated to the county scale and the total number of poultry was divided by the area of the county

Road density

http://www.nationalatlas.gov/atlasftp.html webcite

Calculated as the number roads in each county that connect major population centers

Thaw date (°C)

ftp://sidads.colorado.edu/pub/DATASETS/NOAA/G02156/metadata/ webcite

Calculated as the first day of the year when more than half of the county was not frozen

Total annual precipitation (mm)

http://www.prism.oregonstate.edu/products/matrix.phtml?year0=2000 webcite

Calculated as the average precipitation of all of the 800 m pixels in the county


Fuller et al. BMC Infectious Diseases 2010 10:187   doi:10.1186/1471-2334-10-187

Open Data