This entry will describe the proper narrow and technical meaning of "ecological validity" as proposed by Egon Brunswik as part of the Brunswik Lens Model, the relation of "ecological validity" in "representative design" of research, and will outline the common misuses of the "ecological validity." For a more detailed explanation, see Hammond (1998). Proper Definition of Ecological Validity Egon Brunswik defined the term "ecological validity" in the 1940s to describe a cue's informativeness. The ecological validity of a sensory cue in perception is the regression weight the cue X (something an organism might be able to measure from the proximal stimulus) in predicting a property of the world Y (some aspect of the distal stimulus). The "ecological validity" of X1 is its multiple regression weight when Y is regressed on X1, X2, and X3. For example, the color of a banana is a cue that indicates whether the banana is ripe. This particular cue has high ecological validity because a banana's ripeness is highly correlated with its color. By contrast, the presence of a sticker on the banana is a cue with an ecological validity close to 0, if (as seems likely) ripe and unripe bananas (in a fruit bowl, say) are equally likely to have stickers on them. The concept of ecological validity is closely related to likelihood in Bayesian statistical inference and to cue validity in statistics. Role of "ecological validity" in a "representative design" Brunswik's concept of "ecological validity" is tied to his concept of "representative design." In a "representative design", the variances and correlations of some dependent variable Y and independent variables X1, X2, and X3 match their values in some specific real world ecology. Quoting Hammond (1998), "Generalizability of results concerning. . . the variables involved [in the experiment] must remain limited unless the range, but better also the distribution. . . of each variable, has been made representative of a carefully defined set of conditions" (1956, p. 53). Brunswik's admonition regarding the representativeness of the formal aspects of the conditions of experiments also includes the (ecological) intercorrelation among the independent variables in the experiment, thus challenging the typical factorial design in which variables are set in orthogonal relation to one another." To understand why the "ecological validity" of a cue will change if the design is not "representative", consider two admissions officers, at schools A and B. School A is a highly selective university