This research examined the relationship between subjects' knowledge of an area and their similarity ratings of pairs of concepts. Knowledge was operationalized as (1) test score performance, and (2) correspondence with an expert's similarity judgments. Subjects (n=55) were exposed to a three-week module on social psychology as part of their introductory psychology course. At the end of this course segment they were administered an examination and, later, a term similarity questionnaire. Students' similarity ratings related to both exam score and similarity ratings of the expert. Furthermore, as expected, test performance was strongly related (r=+.55) to the correlation with the expert's similarity judgments. A model based on term similarity judgments was proposed as a theoretical explanation of how term dependence models influence information retrieval system performance.