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. 2015 Feb 17;112(9):2670–2675. doi: 10.1073/pnas.1409606112

Table 1.

Results of test 1, the detection of the impact of long-term climate trends on European crop yields

Row name Wheat yield Maize yield Barley yield Sugar beet yield
Regression coefficient (β1) 0.41 1.39 0.50 0.82
SE 0.10 0.88 0.34 0.81
Test statistic (τ1) 4.03 1.58 1.47 1.00
P(τ1|H0) <0.002 0.002 0.012 0.02
Degrees of freedom 349 267 341 183
Adjusted R2 0.07 0.10 0.06 0.28

The null hypothesis is rejected for all crops at the test size of 5%. Significance levels are determined by a block-bootstrapping procedure that includes resampling the parameters of the climate-yield response function (Methods). Although centered on zero, this distribution is skewed to the left, meaning critical values are lower than under standard normality assumptions [critical values for a one-tailed test under the normal approximation are 1.64 (5%) or 1.28 (10%)].