Refutations of equivocal claims: No evidence for an ironic effect of counterargument number

This study investigated the refutation of equivocal claims using counterarguments. Common sense suggests that more counterarguments should be more effective at inducing belief change. However, some researchers have argued that in persuasive reasoning, using too many arguments might lead to counterproductive skepticism and reactance. Thus, there have been calls to actively curtail the number of counterarguments used in refutations to avoid risking an “overkill backfire effect”—an ironic strengthening of beliefs from too many counterarguments. In three experiments, we tested whether calls to limit the number of counterarguments are justified. We found that a larger number of counterarguments (between four and six) led to as much or more belief reduction compared to a smaller number of (two) counterarguments. This was not merely an effect arising from a simple numerosity heuristic, as counterarguments had to be relevant to affect beliefs: irrelevant counterarguments failed to reduce beliefs even though perceived as moderately persuasive.