Table 2. Variables used in assessing environmental risk for avian influenza in southern Africa. Categories were assigned quantitatively, based on deviations from the mean of a standardised distribution. The reasoning behind the use of these risk factors is discussed in the text.

Variable Description Risk scale
FAOChix Density of chickens per grid cell (FAO 2006) 1=low, 5=high
Popdens1 Human population density (SSA 2001) 1=low, 5=high
Mtemp00 Mean monthly temperature (Hutchinson et al. 1995) 1=warm, 5 = cool
Mrfall00 Mean monthly rainfall (Hutchinson et al. 1995) 1 =low, 5=high
RfallCV Coefficient of variation in mean monthly rainfall (Hutchinson et al. 1995) 1=high (least predictable), 5=low
WL_area Total area of wetlands as defined from 1:50 000 scale map falling into cell (CDSM 2006) 1 = small, 5 = large
WL_perim Total perimeter of wetlands as defined from 1:50 000 scale map falling into cell (CDSM 2006) 1 = small, 5 = large
Grains Area in cell classified as irrigated crops or grasslands in the South African National Land Cover data set (CSIR 2001) 1 = small, 5 = large