Page, Shapiro, and Dempsey: What moves public opinion

Page, Shapiro, and Dempsey. 1987. What moves public opinion?. American Political Science Review 81: 23-44.

Main Argument

A citizen's policy preferences are instrumental, but we are uncertain about the expected costs and benefits of a given policy. Thus, if new information modifies our beliefs about a policy's costs and benefits, we will change our policy preferences. Such a change requires five conditions. The new information must be (see pg 24)

1. received,
2. understood,
3. relevant,
4. at odds with former beliefs, and
5. credible.

Empirical Test

Hypotheses

(Numbers refer to those in the "Main Argument.") Millions of homes watch television news (at least occasionally), thus it is received. Stories are chosen so as to be relevant, and they are presented clearly enough that they can be understood even by pre-teens. The news presents viewpoints from different sources (hence, at odds with former beliefs), each of which has different credibility: the president, commentary, independent experts, and so on. Some stories aren't covered at all, though (control group).

Method

The authors found hundreds of survey questions that had been asked twice (with identical wording) within a couple months (at times T1 and T2). Then, they coded whether the story had been featured on the news before T1 or between T1 and T2. They also coded how prominently it was featured, who the source being quoted was, and so on.

Design

• What to observe: A question about a specific policy was asked twice (with identical wording) at T1 and T2 (a couple months apart).
• X: Before T1, or between T1 and T2, some policies were discussed on the news.
• Y: Answers at T1 relative to T2. Did news coverage change responses at these two times?

Findings

Look at the table on page 30.

Short-term influence: Some groups (the president, opposition, "events") have a negative coefficient in pre-T1 news and a positive coefficient for news between T1 and T2. This suggests that these groups can give public opinion only a short-term boost. News before T1 boosted opinion at T1, but this boost fell off by T2. News between T1 and T2 gave opinion a boost, but you would expect this to fall of by T3.

Long-term influence: Other groups (commentators, experts) appear to have a long-term influence on public opinion: they have a positive coefficient for news pre-T1 (implying that pre-T1 news is still affecting opinion at T2) and an even larger coefficient for news between T1 and T2 (implying an additional short-term influence).

Popular presidents (pg 33) have more influence than unpopular presidents.

Conclusion

Those groups that have the most credibility (news commentators, experts, and popular presidents) also have the most lasting influence on public opinion.