Amelia, D.; Zhafira, A. A.; Ginzel, B. G. C.; Putra, F. Y.; Wibawa, Y. S. Analyzing the Influence of Gross Domestic Product on the Human Development Index Worldwide in 2021 Using a Nonparametric Regression Approach Based on Penalized Spline Estimator. IJCSAM 2025, 11, 68-75.