Accurate measurement of field size is essential for analysis of smallholder survey data

Agronomic surveys play a vital role in identifying on-farm yield constraints and opportunities to increase productivity, input-use efficiency, and farmer profit. These surveys typically rely on farmer-reported data, where crop yield and applied inputs per hectare are estimated based on farmer-reported total harvested output and applied inputs per field and associated field size. At question is how accurate field size is, which is vital in the case of smallholders as small inaccuracies can lead to large biases in estimated yield and inputs. The goals of this study are to assess current approaches to determine field size in smallholders, analyze biases between measurements and farmer estimates, and their influence on the analysis of the survey data. Cost-effective approaches for accurate field size measurement are also discussed. We reviewed published studies that used survey data collected from smallholders to determine the extent to which field size is independently validated by researchers. Subsequently, we used data from thousands of smallholder fields in Southeast Asia to compare farmer-reported versus measured field size and examined the associated impact on estimated yields, inputs, and their relationships. We found that most published studies using survey data did not validate field size reported by farmers. Furthermore, our analysis of the field size data from smallholders in Southeast Asia showed substantial differences between farmer-reported and measured field size, resulting in significant biases in estimated yield and applied inputs, and leading to spurious relationships between them. Uncertainty in field size can mislead analysis of smallholder survey data. Future studies relying on survey data from smallholders should incorporate measurements of field size for accurate determination of crop yield and inputs. •Survey data are used to identify yield constraints in smallholder fields.•Most studies using survey data did not validate farmer-reported field size.•Comparison between farmer and measure field size shows important discrepancies.•Biases between farmer-reported and measured field size lead to erroneous conclusions.•Future studies relying on smallholder survey data should measure field size.