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Table 3 Effect of the environmental variables on AIV cases in wild birds in the contiguous US, 2005-2008.

From: Mapping the risk of avian influenza in wild birds in the US

Effect Est. Std. Err. t-value (df = 132) p
Intercept -3.279 0.58 -5.65 <.0001
First day of the year free of ice or snow Range: 0 (snow-free) to day of the year 150 -0.0282 0.0116 -2.43 0.0164
Minimum temperature Range: -7.15 to 19.67°C -0.2143 0.0734 -2.92 0.0041
Percent harvested cropland per county: Range: 0-100 0.0433 0.00951 4.56 <.0001