Evans School Policy Analysis & Research Group (EPAR)

Common estimates of agricultural productivity rely upon crude measures of crop yield, typically defined as the weight harvested of a crop divided by the area harvested. But this common yield measure poorly reflects performance among farm systems combining multiple crops in one area (e.g., intercropping), and also ignores the possibility that farmers might lose crop area between planting and harvest (e.g., partial crop failure). Drawing on detailed plot-level data from the LSMS-ISA in Tanzania, Nigeria, and Ethiopia, we show how various yield measurement decisions affect estimates of smallholder yields for a variety of crops. We consider the effect of measuring production by plot area, area planted, and area harvested, of trimming the top 1% and 2% of values, and of considering different groups of farmers according to total area planted. 

This brief reviews the various definitions of global public goods (GPGs) and regional public goods (RPGs) found in the literature and provides examples of each in six frequently discussed sectors: environment, health, knowledge, security, governance, and infrastructure. We identify multiple alternative definitions that have gained some traction in the literature, but GPGs are generally agreed to exhibit publicness in consumption, distribution of benefits, and decision-making. Because policy choices determine what is and what is not a GPG, there cannot be a fixed list of such goods; some always have the property of global publicness, while others have over time changed from being local or national to being global in terms of benefits and costs. GPGs are thus redefined as goods that are in the global public domain. GPG and RPG financing mechanisms include payments by users and beneficiaries, taxes, fees, and levies, private funding by non-profit corporations, profit-making firms, and philanthropic individuals and organizations, national and international public resources, and partnerships between several sources of financing. We conclude with an analysis of trends in GPG and RPG financing through Official Development Assistance (ODA) using time series data from the OECD’s Creditor Reporting System and other sources. We find that 14% of ODA in 2014 was allocated to sub-sectors labelled by Reiner et al. as GPGs, while 15% of ODA was allocated to RPGs, and that GPG and RPG spending has steadily increased from 2002-2014.

This brief reviews the evidence of realized yield gains by smallholder farmers attributable to the use of high-quality seed and/or improved seed varieties. Our analysis suggests that in most cases, use of improved varieties and/or quality seed is associated with modest yield increases.  In the sample of 395 trials reviewed, positive yield changes accompanied the use of improved variety or quality seed, on average, in 10 out of 12 crops, with rice and cassava as the two exceptions.

Cassava production is prone to many constraints throughout the production cycle, including biotic, abiotic, and management constraints. This brief reviews the literature on the production impacts of two key cassava stressors: cassava bacterial blight (CBB) and postharvest physiological deterioration (PPD). We summarize available estimates of the frequency and magnitude of these constraints relative to other drivers of cassava production losses that affect smallholder farmers in Sub-Saharan Africa (SSA), review the control strategies proposed in the literature, report on the views of several experts in the field, and identify research gaps where relatively little appears to be known about CBB or PPD yield impacts or best practices for CBB or PPD management.