Table 9. Performance across variations in the functional form.

Functional form	Model specification	Method	MAD	NOTFront	PU20%	PO20%	rs
Linear	θi ∼ unif(0,1)	DEA	0.068	11.8%	0.0%	42.6%	0.863
		rDEA	0.025	2.7%	1.5%	7.2%	0.955
		rSDF-CD	0.106	0.0%	50.2%	10.5%	0.762
		ENS	0.055	0.0%	25.8%	6.3%	0.936
Cobb-Douglas	θi ∼ unif(0,1)	DEA	0.087	11.6%	7.2%	42.0%	0.839
		rDEA	0.095	3.1%	45.4%	12.6%	0.874
		rSDF-CD	0.012	0.0%	0.0%	0.2%	0.997
		ENS	0.045	0.0%	12.6%	7.2%	0.960
Piecewise Cobb-Douglas	θi ∼ unif(0,1)	DEA	0.091	9.5%	16.5%	36.3%	0.836
		rDEA	0.092	2.9%	43.9%	13.3%	0.891
		rSDF-CD	0.012	0.0%	0.0%	0.3%	0.997
		ENS	0.044	0.0%	7.7%	7.5%	0.964

Note: Numbers in bold highlight the best outcome for each performance indicator across the alternative approaches. MAD: median absolute deviation, NOTFront: percentage of misclassified DMUs, PU_20%: percentage of underestimation, PO_20%: percentage of overestimation, r_s: Spearman’s rank correlation.