The control and manipulation of variables in order to test scientific theories. In laboratory-based experiments, it typically involves the manipulation of one variable while attempting to keep all others constant. Outside the laboratory, there are two other types of experiments, with less control over potential confounding variables. One is field experiments carried out in something approaching a natural setting. An example is the study by Niko Tinbergen in 1950 on the selective pecking response of herring gull chicks to the red spot on cardboard model beaks (considered in the past to be a cardinal example of an innate releasing mechanism, but subsequently criticized for methodological shortcomings). Natural experiments constitute the other type and can arise from changes in everyday situations (e.g., changing a school curriculum) and focal cortical lesions (e.g., the well-known case of visual agnosia manifested by Patient DF), the latter constituting something akin to an ‘experiment in nature’. The historical foundations of the experimental method is the subject of some debate. In a western context, claims have been made on behalf of Robert Grosseteste (c.1170-1253) and Roger Bacon (1214-1294).
See Agnosia, Confound, Confounding variable, Control group, Demand characteristics, Double dissociation, Ethology, External validity, Innate releasing mechanism, Internal validity, Ockam’s (or Occam’s) razor, Single-subject experimental design, Still-face paradigm, Validity, Variable