رشيد ظافر حسين, and عبد الحافظ علي سيف الدين. “Comparison Robust M Estimate With Cubic Smoothing Splines For Time-Varying Coefficient Model For Balance Longitudinal Data”. Journal of Economics and Administrative Sciences 19, no. 73 (October 1, 2013): 398. Accessed July 14, 2025. https://www.jeasiq.uobaghdad.edu.iq/index.php/JEASIQ/article/view/1069.