Ecological validity is the extent that a study or its findings can be generalized to natural settings. The concept of ecological validity is particularly relevant to the intersection of cognitive and comparative or developmental psychology. Testing paradigms that are applicable to typically developing human adults are not necessarily adept to measuring the same constructs in different populations (e.g., nonhuman animals, children, individuals with disabilities).
For this reason, tasks must be developed with consideration for "the conditions of the problem without interfering with the natural instincts and proclivities of the animal, and thus distracting or deflecting its attention" (Small, 1900, p. 133). Conclusions about nonhuman animal cognition, for example, have been influenced by the method and tools used in measurement (see Washburn, Rumbaugh, & Putney, 1994).
Small, W. S. (1900). An experimental study of the mental processes of the rat. American Journal of Psychology, 11, 133–165. http://dx.doi.org/10.2307/1412267
Washburn, D. A., Rumbaugh, D. M., & Putney, R. T. (1994). Apparatus as milestones in the history of comparative psychology. Behavior Research Methods, Instruments & Computers, 26(2), 231-235. doi:10.3758/BF03204627