Depth of Issue Coverage in Television News: Campaign ‘84
A study of issue coverage in the evening newscasts of ABC, CBS, CNN, NBC and PBS during the final two weeks of the 1984 Presidential campaign revealed that the four commercial networks tended to frame their issue coverage in a confrontational style, presenting the image of a conflict about the issues by the candidates. However, these stories often failed to identify the positions of the candidates or to give reasons why the candidates supported a particular position. PBS tended to frame its coverage in a confrontational format, but identified and explained candidate issue positions.
Rudd, Robert and Fish, Marjorie J.. (1989). "Depth of Issue Coverage in Television News: Campaign ‘84". Journal of Broadcasting & Electronic Media, 33(2), 197-202.