Okafor, G.I., Agbaeze, E.K., Ekoja, G.O. and Obamen, J. 2018. Effect of six sigma on performance of medium scale manufacturing firms in south-eastern Nigeria. International research journal of management, IT and social sciences. 5, 4 (Jul. 2018), 26–45. DOI:https://doi.org/10.21744/irjmis.v5n4.253.