J. Damanik, Tifany Zia Aznur, and M. Siahaan, “ANALYSIS OF FACTORS AFFECTING LABOR PRODUCTIVITY PALM OIL HARVESTERS AT PT. PERKEBUNAN NUSANTARA IV REGIONAL II BAH BIRUNG ULU GARDEN”, IJSET, vol. 5, no. 8, pp. 4430–4438, Jul. 2026.