A field experiment applies the scientific method to experimentally examine an intervention in the real world (or as many experimentalists like to say, naturally occurring environments) rather than in the laboratory. Field experiments, like lab experiments, generally randomize subjects (or other sampling units) into treatment and control groups and compare outcomes between these groups. Field experiments are so named in order to draw a contrast with laboratory experiments, which enforce scientific control by testing a hypothesis in the artificial and highly controlled setting of a laboratory. Often used in the social sciences, and especially in economic analyses of education and health interventions, field experiments have the advantage that outcomes are observed in a natural setting rather than in a contrived laboratory environment. For this reason, field experiments are sometimes seen as having higher external validity than laboratory experiments. However, like natural experiments, field experiments suffer from the possibility of contamination: experimental conditions can be controlled with more precision and certainty in the lab. Yet some phenomena (e.g., voter turnout in an election) cannot be easily studied in a laboratory.
The use of experiments in the lab and the field have a long history in the physical, natural, and life sciences. Geology has a long history of field experiments, since the time of Avicenna, while field experiments in anthropology date back to Biruni's study of India.Social psychology also has a history of field experiments, including work by pioneering figures Philip Zimbardo, Kurt Lewin and Stanley Milgram. In economics, Peter Bohm, University of Stockholm, was one of the first economists to take the tools of experimental economic methods and attempt to try them with field subjects. In the area of development economics, the pioneer work of Hans Binswanger in the late 1970s conducting experiments in India on risk behavior  should also be noted. The use of field experiments in economics has grown recently with the work of John A. List, Jeff Carpenter, Juan-Camilo Cardenas, Abigail Barr, Catherine Eckel, Michael Kremer, Paul Gertler, Glenn Harrison, Colin Camerer, Bradley Ruffle, Abhijit Banerjee, Esther Duflo, Dean Karlan, Edward "Ted" Miguel, Sendhil Mullainathan, David H. Reiley, among others.
Development economists have used field experiments to measure the effectiveness of poverty and health programs in developing countries. Organizations such as the Abdul Latif Jameel Poverty Action Lab (J-PAL) at the Massachusetts Institute of Technology, the Center of Evaluation for Global Action at the University of California, and Innovations for Poverty Action (IPA) in particular have received attention for their use of randomized field experiments to evaluate development programs. The aim of field experiments used in development research is to find causal relationships between policy interventions and development outcomes. Field experiments are seen by some academics as a rigorous way of testing general theories about economic and political behavior and most recently, field experiments have been used by political scientists to study political behavior, institutional dynamics, and conflict in the developing world.
In a randomized field experiment on an international development intervention, researchers would separate participants into two or more groups: a treatment group (or groups) and a control group. Members of the treatment group(s) then receive a particular development intervention being evaluated while the control group does not. (Often the control group receives the intervention later in the roll out of the study.) Field experiments have gained popularity in the field because they allow researchers to guard against selection bias, a problem present in many current studies of development interventions. Selection bias refers to the fact that, in non-experimental settings, the group receiving a development intervention is likely different from a group that is not receiving the intervention. This may occur because of characteristics that make some people more likely to opt into a program, or because of program targeting. Some academics dispute the claim that findings from field experiments are sufficient for establishing and testing theories about behavior. In particular, a hotly contested issue with regards to field experiments is their external validity. Given that field experiments necessarily take place in a specific geographic and political setting, the extent to which findings can be extrapolated to formulate a general theory regarding economic behavior is a concern.