McCombs and Shaw in their study The Agenda-Setting Function of Mass Media made an arguments that the mass media set the agenda for each political campaign, influencing the salience of attitudes toward the political issues, because the media appeared to have exerted a considerable impact on voters' judgments of what they considered the major issues of the campaign, based on the finds from the Chapel Hill voters survey in 1968 that there were strong correlation between the major item emphasis on the main campaign issues carried by the media and voters' independent judgments of what were the important issues.
In Tichenor, Donohue, and Olien’s study Mass Media Flow and Differential Growth in Knowledge, they made an argument that as the infusion of mass media information into a social system increased, segments of the population with higher socioeconomic status tended to acquire this information at a faster rate than the lower status segments, so that the gap in knowledge between these segments tended to increase rather than decrease, because the mass media had a function similar to that of other social institutions: that of reinforcing or increasing existing inequities, and highly educated persons were more likely to have been exposed to a heavily publicized topic in the past, based on the findings from one experiment which indicated a correlation between education and the understanding of certain issues with different levels of publicity.
In a following research of Tichenor, Donohue, and Olien, Mass Media and the Knowledge Gap: A Hypothesis Reconsidered, they found in the surveys that for the sixteen Minnesota communities as a whole, the size of the knowledge gap was only weakly related to the newspaper coverage index and in a negative direction. These findings suggested that the original hypothesis, however well supported by previous data, may not hold for all situations. So they made several modifications of the general knowledge gap hypothesis by employing some new variables:
1. Where the issue appears to arouse general concern for a community as a whole, knowledge about that issue is more likely to become evenly distributed across educational status levels.
2. This equalization is more likely to occur when the issue develops in a climate of social conflict.
3. Such equalization in knowledge is more likely to occur in a small, homogeneous community than in a large, pluralistic one.
4. Knowledge gaps on specific issues, if they appear initially, may tend to decline as public attention wanes.