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In research, the ecological validity of a study means that the methods, materials and setting of the study must approximate the real-world that is being examined. Unlike internal and external validity, ecological validity is not necessary to the overall validity of a study.[not specific enough to verify]
Ecological validity is often confused with external validity (which deals with the ability of a study's results to generalize). While these forms of validity are closely related, they are independent—a study may possess external validity but not ecological validity, and vice versa. For example, mock-jury research is designed to study how people might act if they were jurors during a trial, but many mock-jury studies simply provide written transcripts or summaries of trials, and do so in classroom or office settings. Such experiments do not approximate the actual look, feel and procedure of a real courtroom trial, and therefore lack ecological validity. However, the more important concern is that of external validity—if the results from such mock-jury studies generalize to real trials, then the research is valid as a whole, despite its ecological shortcomings. Nonetheless, improving the ecological validity of an experiment typically improves the external validity as well.
The original meaning of 'ecological validity' defines it more narrowly as a property of stimuli in perceptual experiments. The popular use, broadly equivalent to 'realism', has overtaken it, at least in A Level Psychology circles. For the original (and some feel correct) use, see the entry on 'ecological validity - perception' and especially the paper by Hammond, 1998, which is referred to there. This can be accessed at: http://www.albany.edu/cpr/brunswik/notes/essay2.html . 'Representative design' captures the popular usage of ecological validity and can be used in its place.