Fig. 3. Relationship between UV and human-visible dichromatism. Geometric mean regression of PCA estimates of dichromatism in the UV range (320–400 nm) against human visual estimates (r²=0.25, N=960, P<0.0001). PCA scores were calculated using spectrophotometer data and human-visible scores are from the study of Dunn and colleagues (Dunn et al., 2001). Scores for each index were standardized to a mean of zero and a standard deviation of one.