Oktarina, C. R., S. Nugroho, and I. Sriliana. “EVALUATION OF THE FLEXIBILITY OF NADARAYA-WATSON KERNEL AND PENALIZED SPLINE ESTIMATORS IN BIVARIATE RESPONSE NONPARAMETRIC REGRESSION MODELS”. BAREKENG: Jurnal Ilmu Matematika Dan Terapan, Vol. 20, no. 3, Apr. 2026, pp. 2179-94, doi:10.30598/barekengvol20iss3pp2179-2194.