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Field experiments are
experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs whe ...
s carried out outside of
laboratory A laboratory (; ; colloquially lab) is a facility that provides controlled conditions in which scientific or technological research, experiments, and measurement may be performed. Laboratory services are provided in a variety of settings: physi ...
settings. They randomly assign subjects (or other sampling units) to either treatment or control groups in order to test claims of
causal Causality (also referred to as causation, or cause and effect) is influence by which one event, process, state, or object (''a'' ''cause'') contributes to the production of another event, process, state, or object (an ''effect'') where the ca ...
relationships. Random assignment helps establish the comparability of the treatment and control group, so that any differences between them that emerge after the treatment has been administered plausibly reflect the influence of the treatment rather than pre-existing differences between the groups. The distinguishing characteristics of field experiments are that they are conducted real-world settings and often unobtrusively. This is in contrast to laboratory experiments, which enforce scientific control by testing a hypothesis in the artificial and highly controlled setting of a laboratory. Field experiments have some contextual differences as well from naturally-occurring experiments and quasi-experiments. While naturally-occurring experiments rely on an external force (e.g. a government, nonprofit, etc.) controlling the randomization treatment assignment and implementation, field experiments require researchers to retain control over randomization and implementation. Quasi-experiments occur when treatments are administered as-if randomly (e.g. U.S. Congressional districts where candidates win with slim-margins, weather patterns, natural disasters, etc.). Field experiments encompass a broad array of experimental designs, each with varying degrees of generality. Some criteria of generality (e.g. authenticity of treatments, participants, contexts, and outcome measures) refer to the contextual similarities between the subjects in the experimental sample and the rest of the population. They are increasingly used in the social sciences to study the effects of policy-related interventions in domains such as health, education, crime, social welfare, and politics.


Characteristics

Under random assignment, outcomes of field experiments are reflective of the real-world because subjects are assigned to groups based on non-deterministic probabilities. Two other core assumptions underlie the ability of the researcher to collect unbiased potential outcomes: excludability and non-interference. The excludability assumption provides that the only relevant causal agent is through the receipt of the treatment. Asymmetries in assignment, administration or measurement of treatment and control groups violate this assumption. The non-interference assumption, or Stable Unit Treatment Value Assumption (SUTVA), indicates that the value of the outcome depends only on whether or not the subject is assigned the treatment and not whether or not other subjects are assigned to the treatment. When these three core assumptions are met, researchers are more likely to provide unbiased estimates through field experiments. After designing the field experiment and gathering the data, researchers can use
statistical inference Statistical inference is the process of using data analysis to infer properties of an underlying distribution of probability.Upton, G., Cook, I. (2008) ''Oxford Dictionary of Statistics'', OUP. . Inferential statistical analysis infers properti ...
tests to determine the size and strength of the intervention's effect on the subjects. Field experiments allow researchers to collect diverse amounts and types of data. For example, a researcher could design an experiment that uses pre- and post-trial information in an appropriate statistical inference method to see if an intervention has an effect on subject-level changes in outcomes.


Practical uses

Field experiments offer researchers a way to test theories and answer questions with higher
external validity External validity is the validity of applying the conclusions of a scientific study outside the context of that study. In other words, it is the extent to which the results of a study can be generalized to and across other situations, people, stim ...
because they simulate real-world occurrences. Some researchers argue that field experiments are a better guard against potential
bias Bias is a disproportionate weight ''in favor of'' or ''against'' an idea or thing, usually in a way that is closed-minded, prejudicial, or unfair. Biases can be innate or learned. People may develop biases for or against an individual, a group ...
and biased estimators. As well, field experiments can act as benchmarks for comparing observational data to experimental results. Using field experiments as benchmarks can help determine levels of bias in observational studies, and, since researchers often develop a hypothesis from an
a priori ("from the earlier") and ("from the later") are Latin phrases used in philosophy to distinguish types of knowledge, justification, or argument by their reliance on empirical evidence or experience. knowledge is independent from current ex ...
judgment, benchmarks can help to add credibility to a study. While some argue that covariate adjustment or matching designs might work just as well in eliminating bias, field experiments can increase certainty by displacing omitted variable bias because they better allocate observed and unobserved factors. Researchers can utilize machine learning methods to simulate, reweight, and generalize experimental data. This increases the speed and efficiency of gathering experimental results and reduces the costs of implementing the experiment. Another cutting-edge technique in field experiments is the use of the multi armed bandit design, including similar adaptive designs on experiments with variable outcomes and variable treatments over time.


Limitations

There are limitations of and arguments against using field experiments in place of other research designs (e.g. lab experiments, survey experiments, observational studies, etc.). Given that field experiments necessarily take place in a specific geographic and political setting, there is a concern about extrapolating outcomes to formulate a general theory regarding the population of interest. However, researchers have begun to find strategies to effectively generalize causal effects outside of the sample by comparing the environments of the treated population and external population, accessing information from larger sample size, and accounting and modeling for treatment effects heterogeneity within the sample. Others have used covariate blocking techniques to generalize from field experiment populations to external populations. Noncompliance issues affecting field experiments (both one-sided and two-sided noncompliance) can occur when subjects who are assigned to a certain group never receive their assigned intervention. Other problems to data collection include attrition (where subjects who are treated do not provide outcome data) which, under certain conditions, will bias the collected data. These problems can lead to imprecise data analysis; however, researchers who use field experiments can use statistical methods in calculating useful information even when these difficulties occur. Using field experiments can also lead to concerns over interference between subjects. When a treated subject or group affects the outcomes of the nontreated group (through conditions like displacement, communication, contagion etc.), nontreated groups might not have an outcome that is the true untreated outcome. A subset of interference is the spillover effect, which occurs when the treatment of treated groups has an effect on neighboring untreated groups. Field experiments can be expensive, time-consuming to conduct, difficult to replicate, and plagued with ethical pitfalls. Subjects or populations might undermine the implementation process if there is a perception of unfairness in treatment selection (e.g. in ' negative income tax' experiments communities may lobby for their community to get a cash transfer so the assignment is not purely random). There are limitations to collecting consent forms from all subjects. Comrades administering interventions or collecting data could contaminate the randomization scheme. The resulting
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
, therefore, could be more varied: larger
standard deviation In statistics, the standard deviation is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean (also called the expected value) of the set, whil ...
, less
precision and accuracy Accuracy and precision are two measures of ''observational error''. ''Accuracy'' is how close a given set of measurements (observations or readings) are to their ''true value'', while ''precision'' is how close the measurements are to each other ...
, etc. This leads to the use of larger
sample size Sample size determination is the act of choosing the number of observations or replicates to include in a statistical sample. The sample size is an important feature of any empirical study in which the goal is to make inferences about a populati ...
s for field testing. However, others argue that, even though replicability is difficult, if the results of the experiment are important then there a larger chance that the experiment will get replicated. As well, field experiments can adopt a " stepped-wedge" design that will eventually give the entire sample access to the intervention on different timing schedules. Researchers can also design a blinded field experiment to remove possibilities of manipulation.


Examples

The history of experiments in the lab and the field has left longstanding impacts in the physical, natural, and life sciences. Modern use field experiments has roots in the 1700s, when James Lind utilized a controlled field experiment to identify a treatment for
scurvy Scurvy is a deficiency disease, disease resulting from a lack of vitamin C (ascorbic acid). Early symptoms of deficiency include weakness, feeling tired and sore arms and legs. Without treatment, anemia, decreased red blood cells, gum disease, ch ...
. Other categorical examples of sciences that use field experiments include: *
Economists An economist is a professional and practitioner in the social science discipline of economics. The individual may also study, develop, and apply theories and concepts from economics and write about economic policy. Within this field there are ...
have used field experiments to analyze
discrimination Discrimination is the act of making unjustified distinctions between people based on the groups, classes, or other categories to which they belong or are perceived to belong. People may be discriminated on the basis of Racial discrimination, r ...
(e.g., in the labor market, in housing, in the sharing economy, in the credit market, or in integration),
health care Health care or healthcare is the improvement of health via the prevention, diagnosis, treatment, amelioration or cure of disease, illness, injury, and other physical and mental impairments in people. Health care is delivered by health pr ...
programs, charitable fundraising,
education Education is a purposeful activity directed at achieving certain aims, such as transmitting knowledge or fostering skills and character traits. These aims may include the development of understanding, rationality, kindness, and honesty ...
, information aggregation in markets, and
microfinance Microfinance is a category of financial services targeting individuals and small businesses who lack access to conventional banking and related services. Microfinance includes microcredit, the provision of small loans to poor clients; savings ...
programs. *
Engineer Engineers, as practitioners of engineering, are professionals who Invention, invent, design, analyze, build and test machines, complex systems, structures, gadgets and materials to fulfill functional objectives and requirements while considerin ...
s often conduct field tests of
prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and software programming. A prototype is generally used to ...
products to validate earlier laboratory tests and to obtain broader feedback. *
Anthropology Anthropology is the scientific study of humanity, concerned with human behavior, human biology, cultures, societies, and linguistics, in both the present and past, including past human species. Social anthropology studies patterns of be ...
field experiments date back to
Biruni Abu Rayhan Muhammad ibn Ahmad al-Biruni (973 – after 1050) commonly known as al-Biruni, was a Khwarazmian Iranian in scholar and polymath during the Islamic Golden Age. He has been called variously the "founder of Indology", "Father of Co ...
's study of India. *
Social psychology Social psychology is the scientific study of how thoughts, feelings, and behaviors are influenced by the real or imagined presence of other people or by social norms. Social psychologists typically explain human behavior as a result of the ...
has pioneering figures who utilized field experiments, including
Kurt Lewin Kurt Lewin ( ; 9 September 1890 – 12 February 1947) was a German-American psychologist, known as one of the modern pioneers of social, organizational, and applied psychology in the United States. During his professional career Lewin applied hi ...
and
Stanley Milgram Stanley Milgram (August 15, 1933 – December 20, 1984) was an American social psychologist, best known for his controversial experiments on obedience conducted in the 1960s during his professorship at Yale.Blass, T. (2004). ''The Man Who Shock ...
. *
Agricultural science Agricultural science (or agriscience for short) is a broad multidisciplinary field of biology that encompasses the parts of exact, natural, economic and social sciences that are used in the practice and understanding of agriculture. Profession ...
researcher R.A. Fisher analyzed randomized actual "field" experimental data for crops. *
Political Science Political science is the scientific study of politics. It is a social science dealing with systems of governance and power, and the analysis of political activities, political thought, political behavior, and associated constitutions and ...
researcher Harold Gosnell conducted an early field experiment on voter participation in 1924 and 1925. *
Ecology Ecology () is the study of the relationships between living organisms, including humans, and their physical environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere level. Ecology overl ...
Joseph H. Connell’s field experiment.


See also

*
Field research Field research, field studies, or fieldwork is the collection of raw data outside a laboratory, library, or workplace setting. The approaches and methods used in field research vary across disciplines. For example, biologists who conduct f ...
*
Experiment An experiment is a procedure carried out to support or refute a hypothesis, or determine the efficacy or likelihood of something previously untried. Experiments provide insight into cause-and-effect by demonstrating what outcome occurs whe ...


References

{{DEFAULTSORT:Field Experiment Design of experiments Tests Causal inference Mathematical and quantitative methods (economics) Field research