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	Mother-Baby Trial Design	Land Equivalent Ratio
Field	Food Agriculture Studies	Food Agriculture Studies
Family	Process / pipeline	Process / pipeline
Year of origin	2002	1980
Originator	Sieglinde Snapp	Roger Mead & Roger W. Willey
Type	Linked on-farm experimental design pairing replicated and dispersed trials	Descriptive index of relative land productivity
Seminal source	Snapp, S. (2002). Quantifying Farmer Evaluation of Technologies: The Mother and Baby Trial Design. In M. R. Bellon & J. Reeves (Eds.), Quantitative Analysis of Data from Participatory Methods in Plant Breeding (pp. 9-17). Mexico, DF: CIMMYT.	Mead, R., & Willey, R. W. (1980). The Concept of a 'Land Equivalent Ratio' and Advantages in Yields from Intercropping. Experimental Agriculture, 16(3), 217-228.
Aliases	Mother and Baby Trial Design, MBT Design, Mother-Baby Trial Approach, Mother-Baby On-Farm Trials	LER, Relative Yield Total, Land Equivalent Coefficient, Intercropping Land-Use Efficiency
Related	4	4
Summary	The mother-baby trial design is an on-farm experimental architecture, formalized by Sieglinde Snapp in 2002, that resolves the long-standing tension between statistical rigor and wide farmer participation in agricultural research. A small number of replicated 'mother' trials carry the complete set of treatments under good management and provide the controlled, analyzable comparison; surrounding them, a large number of simple 'baby' trials, each on a farmer's own field and each testing only a subset of the treatments against the farmer's usual practice, sample the real variation in conditions and capture farmer evaluation at scale. Linking the two — the mother for precision, the babies for breadth and realism — yields both defensible treatment estimates and credible evidence about how technologies perform and are judged across many real farms.	The land equivalent ratio (LER) is the standard index for judging whether intercropping — growing two or more crops together on the same land — uses land more efficiently than growing each crop separately. Formalized by Roger Mead and Roger Willey in 1980, the LER expresses how much land would be required under sole cropping to produce the yields achieved by one unit of intercropped land. It is computed by dividing each component crop's intercrop yield by its sole-crop yield and summing these partial ratios across all components. An LER greater than one means the intercrop is more land-efficient than the corresponding sole crops, and the amount above one quantifies the land saved, giving agronomists a simple, interpretable, and widely used measure of the biological advantage of mixed cropping.