Elshafei, A. (1968). Product Performance Models PPM. The Institute of National Planning.
Citazione stile Chigago Style (17a edizione)Elshafei, Alwalid. Product Performance Models PPM. Cairo: The Institute of National Planning, 1968.
Citatione MLA (9a ed.)Elshafei, Alwalid. Product Performance Models PPM. The Institute of National Planning, 1968.
Attenzione: Queste citazioni potrebbero non essere precise al 100%.