@INBOOK {SPENCER:1991a,
title = {Collecting meaningful data on labor use and farm size for economic analysis associated with on-farm trials in sub-Saharan African},
author = {Spencer, D. },
year = {1991},
type = {On-farm research in theory and practice, edited by H.J.W. Mutsaers and P. Walker},
pages = {53--59},
publisher = {International Institute of Tropical Agriculture (IITA)},
address = {Ibadan, Nigeria},
}