Fifty-eight studies relating to the "knowledge gap" hypothesis (a theory that correlates public knowledge to educational level and mass media exposure) are examined in this report. In the opening sections, the theory is defined, and the early information diffusion studies and public opinion polls that led to its formulation in 1970 are described. In the next sections, pertinent qualities of all the published and unpublished knowledge gap studies are identified and treated as variables for the construction of a table of conclusions about the validity of the hypothesis. These characteristics include (1) date and location of research, (2) sample size, (3) completion rate, (4) type of population, (5) research design, (6) number of measurements in time, (7) method of data collection, (8) topic studies, (9) type of knowledge studied (awareness or depth), (10) operational definitions of education and knowledge gap, (11) an assessment of amount of media publicity involved, and (12) knowledge gap findings (education/knowledge data). The report points out that the data reveal that the theory's proposition--the higher the education, the greater the knowledge of various topics--is supported by most of the studies, but its other proposal about the correlation between knowledge and mass media levels is not. Future considerations for research follow the conclusions, as do three tables in which the review data are presented and summarized. (JL)