Onu OH, Ejukwa JO, Nanaka S. A comparative study of the performance of cubic and quadratic models for heptagonal spherical two-factor second-order designs based on the sum of square errors. FNAS-JSI [Internet]. 2023 Mar. 30 [cited 2024 Nov. 23];4(1):140-8. Available from: https://fnasjournals.com/index.php/FNAS-JSI/article/view/129