Hovland, C. I., & Weiss, W., The Influence of Source Credibility
on Communication Effectiveness, Public Opinion Quarterly, 1951, 15, 635-650.
In this study the researchers found that material initially rejected
as coming from untrustworthy sources was eventually disassociated (source
from data) and later accepted as truth. Lies seemed to be remembered better
than truths.
This study was designed to test the level of retention and acquisition of
identical communications when presented by "trustworthy" and "untrustworthy"
sources.
They gave opinion questionnaires before, immediately after, and one month
after the communication. Each topic had positive and negative articles
about it coming from either highly credible news source (scientific journal,
etc. ) or a low credible new source (tabloid, etc.).
They arranged four articles (with sources) in a small booklet. Yale undergraduates
read the booklets and filled out opinion questionnaires about them (plus
some questions testing recall).
Results
In 14 of 16 possible comparisons the low credibility sources were judged
less-fair or less justified than the high credibility sources (though the
articles were identical). There was much higher opinion approvals for
the high credibility sources, and people changed their opinions to a greater
extent with high than low credibility sources. However, there was no difference
in retention based on credibility levels.
Retention of Opinion
Interestingly, over time there is a decrease in agreement with the high
credibility source, and an increase in agreement with a low credibility
source. Their occured a "sleeper effect", where people who initially
disagree with a statement by a source will forget who gave the statement
and eventually change their opinion more in favor of it.
Conclusion
It seems the content of communication is is learned and forgotten to the
same extent regardless of the communicator. But the extent of opinion change
is influenced by both learning and acceptance, and the effect of an untrustworthy
communicator is to interfere with the acceptance of the material. However,
this interference is decreased with time (even to the extent where the long-term
opinion orginating from a high or low credibility source are the same).
In the high credible case people forget the content and drop their opinion.
In the other case they forget the source of the low credible data and thus
have a better feeling for the information and thus change their opinion.