Missing(ness) in Action : Selectivity Bias in GPS-Based Land Area Measurements

Land area is a fundamental component of agricultural statistics, and of analyses undertaken by agricultural economists. While household surveys in developing countries have traditionally relied on farmers' own, potentially error-prone, land area assessments, the availability of affordable and reliable Global Positioning System (GPS) units has made GPS-based area measurement a practical alternative. Nonetheless, in an attempt to reduce costs, keep interview durations within reasonable limits, and avoid the difficulty of asking respondents to accompany interviewers to distant plots, survey implementing agencies typically require interviewers to record GPS-based area measurements only for plots within a given radius of dwelling locations. It is, therefore, common for as much as a third of the sample plots not to be measured, and research has not shed light on the possible selection bias in analyses relying on partial data due to gaps in GPS-based area measures. This paper explores the patterns of missingness in GPS-based plot areas, and investigates their implications for land productivity estimates and the inverse scale-land productivity relationship. Using Multiple Imputation (MI) to predict missing GPS-based plot areas in nationally-representative survey data from Uganda and Tanzania, the paper highlights the potential of MI in reliably simulating the missing data, and confirms the existence of an inverse scale-land productivity relationship, which is strengthened by using the complete, multiply-imputed dataset. The study demonstrates the usefulness of judiciously reconstructed GPS-based areas in alleviating concerns over potential measurement error in farmer-reported areas, and with regards to systematic bias in plot selection for GPS-based area measurement.

Bibliographic Details

Main Authors:	Kilic, Talip, Zezza, Alberto, Carletto, Calogero, Savastano, Sara
Language:	English en_US
Published:	World Bank, Washington, DC 2013-06
Subjects:	AGRICULTURAL OUTPUT, AGRICULTURE, COMMODITY, COMPUTATION, CONFIDENCE INTERVALS, COVARIANCE, COVARIANCE MATRIX, DATA ANALYSES, DATA ANALYSIS, DATA COLLECTION, DATA ENTRY, DESCRIPTIVE STATISTICS, DEVELOPMENT ECONOMICS, DEVELOPMENT POLICY, DEVELOPMENT RESEARCH, DEVELOPMENT STRATEGIES, DOMAIN, DOMAINS, ECONOMIC DEVELOPMENT, ECONOMIC INEQUALITY, ENUMERATION, EQUIPMENT, EXPERIMENTS, EXPLORATION, FIELD WORK, FINANCIAL RESOURCES, FINANCIAL SUPPORT, GLOBAL POSITIONING SYSTEM, GPS, GROSS VALUE, HUMAN RESOURCES, HYPOTHESIS TESTING, IMPLEMENTING AGENCIES, IMPUTATION METHOD, IMPUTATION METHODS, IMPUTATION PROCESS, IMPUTATIONS, INCOME, INDEPENDENT VARIABLES, INNOVATION, LINEAR PREDICTION, LINEAR REGRESSION, LIVING STANDARDS, MEASUREMENT ERRORS, MISSING DATA, MISSING OBSERVATIONS, MISSING VALUE, MISSING VALUES, MULTIPLE IMPUTATION, OPEN ACCESS, OPPORTUNITY COSTS, POLITICAL ECONOMY, PRECISION, PREDICTIONS, PROBABILITY, PRODUCTION FUNCTION, PRODUCTIVITY, PROPERTY RIGHTS, PROTOCOL, PROTOCOLS, QUALITY CONTROL, QUESTIONNAIRES, RESEARCH METHODS, RESEARCH REPORT, RESEARCH WORKING PAPERS, RESEARCHERS, RESULT, RESULTS, SAMPLE SIZE, SAMPLE SURVEYS, SATELLITE, SCIENCES, SENSITIVITY ANALYSIS, SIMULATIONS, SOFTWARE PACKAGES, STANDARD ERRORS, STANDARD MEASUREMENT, STATA, STATISTICAL ANALYSES, STATISTICAL INFERENCE, STATISTICAL TECHNIQUES, STATISTICIANS, SUPERVISION, SURPLUS LABOR, SURVEY DATA, SURVEY DESIGN, SURVEYORS, TECHNOLOGICAL INNOVATIONS, TOTAL FACTOR PRODUCTIVITY, TOTAL OUTPUT, TRANSITION ECONOMY, USE VALUE, USERS, VALIDITY, VALUE OF OUTPUT, VARIABILITY, WEALTH, WEB, WEIGHTING, land area measurement, land productivity,
Online Access:	http://documents.worldbank.org/curated/en/2013/06/17875976/missingness-action-selectivity-bias-gps-based-land-area-measurements https://hdl.handle.net/10986/15849
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