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Table 2 Results from 11 linear mixed-effects models explaining the relationship between age, calculated from molar exams, and each of the 11 tusk to body size ratios, calculated from images, with a natural cubic spline (d.f. = 3) and individuals as random effects. *represents explanatory variables with significant p values (< 0.05) for all three cubic spline values. n = 11 individuals

From: Mining morphometrics and age from past survey photographs

Explanatory variable (ratio) Cubic spline Value Standard error DF p value
Tusk length: body length 1 0.060 0.071 43 0.399
2 0.330 0.169 43 0.058
3 0.277 0.071 43 < 0.001
Tusk length: body height 1 0.165 0.046 40 0.001*
2 0.377 0.118 40 0.003*
3 0.340 0.047 40 < 0.001
Tusk length: foot diameter 1 0.530 0.308 40 0.093
2 1.80 0.751 40 0.021
3 1.71 0.308 40 < 0.001
Tusk length: head height 1 0.610 0.251 40 0.019*
2 1.25 0.617 40 0.050*
3 1.65 0.251 40 < 0.001
Tusk length: head girth 1 −2.96 1.86 40 0.120*
2 4.75 2.13 40 0.031*
3 6.70 0.979 40 < 0.001
Tusk length: tusk diameter 1 4.02 1.33 40 0.004*
2 8.05 3.44 40 0.024*
3 9.31 1.35 40 < 0.001
Tusk diameter: body length 1 0.011 0.006 40 0.098
2 0.023 0.013 40 0.080
3 0.007 0.006 40 0.204
Tusk diameter: body height 1 0.002 0.006 40 0.731
2 0.007 0.015 40 0.662
3 −0.013 0.006 40 0.033
Tusk diameter: foot diameter 1 0.041 0.032 40 0.202
2 0.094 0.069 40 0.181
3 0.012 0.030 40 0.690
Tusk diameter: head height 1 0.026 0.025 40 0.315
2 −0.007 0.061 40 0.911
3 −0.012 0.025 40 0.646
Tusk diameter: head girth 1 −0.334 0.225 40 0.146
2 0.442 0.236 40 0.068
3 0.500 0.106 40 < 0.001