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. 2008 Feb 6;3(2):e1552. doi: 10.1371/journal.pone.0001552

Figure 3. Annual evolution of WR relative improvement: κ decreases from 0.024 in the first 30 years to 0.010 in the last 10 years (Linear model: y = −1.46·10−4 x+0.301, F(1,102) = 27.14, P<0.001).

Figure 3

This decrease is representative of the growing difficulty to improve previously established WR values.