Table 2. $R^2$ values for the exponential regression model for different feature inputs and sample sizes.

Sample size	ψ	${\beta }_1$	$\left({\psi }^2,{\beta }_1^2,\psi ,{\beta }_1,\text{Φ}\right)$
25	0.724	0.456	0.792
50	0.847	0.749	0.894
75	0.883	0.827	0.927
95	0.898	0.862	0.941
140	0.909	0.887	0.959
Mixed	0.414	0.164	0.851