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.
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Variable |
Description |
Risk scale |
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FAOChix |
Density of chickens per grid cell (FAO 2006) |
1=low, 5=high |
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Popdens1 |
Human population density (SSA 2001) |
1=low, 5=high |
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Mtemp00 |
Mean monthly temperature (Hutchinson et al. 1995) |
1=warm, 5 = cool |
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Mrfall00 |
Mean monthly rainfall (Hutchinson et al. 1995) |
1 =low, 5=high |
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RfallCV |
Coefficient of variation in mean monthly rainfall (Hutchinson et al.
1995) |
1=high (least predictable), 5=low |
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WL_area |
Total area of wetlands as defined from 1:50 000 scale map falling into
cell (CDSM 2006) |
1 = small, 5 = large |
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WL_perim |
Total perimeter of wetlands as defined from 1:50 000 scale map falling
into cell (CDSM 2006) |
1 = small, 5 = large |
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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 |
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