@INBOOK {SMITH:1991, title = {Representativeness of farmers and sites in on-farm trials}, author = {Smith, J. and Walker, P. and Oyewole, B. }, year = {1991}, type = {On-farm research in theory and practice, edited by H.J.W. Mutsaers and P. Walker}, pages = {83--94}, publisher = {International Institute of Tropical Agriculture (IITA)}, address = {Ibadan, Nigeria}, }