Lord, C., Ross, L., & Lepper, M., Biased Assimilation and Attitude
Polarization: The effects of Prior Theories on Subsequently Considered
Evidence. JPSP, 1979, 37, 2098-2109.
"People who hold strong opinions on complex social issues are
likely to examine relevant empirical evidence in a biased manner. They
are apt to accept "confirming" evidence at face value while sujecting
"disconfirming" evidence to critical evaluation, and as a result
to draw undue support for their initial position from mixed or random empirical
Thus the result of exposure to a group holding different views can be polarization
This result was confirmed using two variations of studies on the death
Often opinions on important social issues often "survive strenuous
attempts at resolution through discussion and persuation". However
data relevant to a belief are not processes impartially. People accept
the data that suports their initial beliefs and rejects the information
that doesn't support it, leaving them even more convinced of their opinions.
It's called a "biased assimilation process". People can:
* remember strenghts of confirming data but weaknesses of disconfirming
* judge confirming data reliable and disconfirmaining data unreliable
Based on questionnaire information, they selected 24 proponents and 24 opponents
to the death penality (undergraduate psych students). In groups they individually
read cards with either confirming or disconfirming results of studies about
the death penality. They read the cards and then answered questions about
attitude change. Then they read the full procedures and results of each
study and then judged how through and accurate each study was. Then they
answered attitude change quesitons again. They repeated the procedure with
another study with opposite results.
There was strong bias toward the report that matched their initial opinion
on the death penalty. There was also more polarization in attitude at the
end of the experiment.
Interestingly, after exposure to only one study, both groups move toward
the findings from the data, but they more affected those who were already
predisposed to the position. When they reviewed the full studies, they
tended to ignore the final results and found data within each study (either
confirming data or disconfirming flaws in the experiment) to support their
initial beliefs. Any initial swaying at first by just reviewing the results
was eliminated when they examined the entire procedure.
This shows how people can find pieces of data in any study to bolster and
continue their views, even when the bulk of the information is to the contrary.
Other studies confirm that people can persist in their beliefs even when
all of the evidence is discredited.
It shows that social scientists should not expect that rationality, elightenment
and consensus to emerge when they publish new "conclusive" data
about an important social issue.