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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