Definition

The dilution effect is a judgment bias in which people underutilize diagnostic information when nondiagnostic information is also present. Diagnostic information is knowledge that is useful in making a particular judgment. Nondiagnostic information is knowledge that is not relevant to the judgment being made. For example, if a medical doctor were making a judgment about a patient's condition, the patient's symptoms would be diagnostic information. The doctor might also know the patient's hair color, but because this information would not be useful in judging the patient's condition, it would be nondiagnostic.

When both kinds of information are present, people tend to underrely on diagnostic information in making judgments. Thus, the presence of nondiagnostic information weakens, or dilutes, the impact of diagnostic information on judgment. The dilution ...