Lens Model

Distal Variable

On the left side of the lens model is the distal variable (Ye), also called the criterion. It represents an event or observation that is the focus of judgment, such as the presence of a disease, the severity of an illness, or the correct dosage of a drug. In medicine, this is often called the gold standard. It is “distal” relative to the person making a judgment because it is not directly available to him or her.

Cues

The cues (X) are the surface data that are available for making inferences about the distal variable. The cues include, for example, the symptoms, features of images, or test results that are available to the person at the time the judgment is made. The cues are imperfect. They may be subject to measurement error, and they may lack some of the information needed to make an ideal judgment. This limitation is common in judgment situations that occur in medicine.

Judgment

On the right side of the lens model is the judgment (Ys), which is usually considered to be continuous. If the distal variable is continuous, then the judgment is measured in the same units as the distal variable. If the distal variable is binary or categorical, then the judgment is usually thought of as a probability. In either case, the judgment represents a person's attempt, implicitly or explicitly, to assess or predict the value of the distal variable, either in the present or at some future time. The judgment is assumed to be empirically verifiable, at least in principle. Judgment is necessary because the distal variable is not directly observable, either because it is obscured or hidden in some way or because it occurs in the future. Judgments of preference or value, such as how pleasing a painting is, or the desirability of a dessert item, are not addressed by the lens model.

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