“…Indeed, previous studies on this subject, for example, Hailu et al [ 20 ], Ainembabazi et al [ 3 ], and Wollni and Brümmer [ 21 ] assume that the decision to participate in cooperatives or otherwise is random and may not be affected by unobserved factors. A few studies related to this subject in Nigeria, to our utmost knowledge, also follow suit on this assumption and consequently included cooperative membership as an explanatory variable in the efficiency model (for example [ 23 , 24 ]). However, in reality, farmer’s decision to join cooperatives is non-random which simply implies that such a decision is based on the individual farmer’s self-selection into membership.…”