B. I. Putra and A. Y. Ardiansah, “Operational Productivity Index Patterns in Logistics Services Using Mundel Model: Pola Indeks Produktivitas Operasional dalam Layanan Logistik Menggunakan Model Mundel”, ijler, vol. 20, no. 3, p. 10.21070/ijler.v20i3.1505, Feb. 2026.