Psychologists increasingly recommend experimental analysis of mediation. This is a step in the right direction because mediation analyses based on nonexperimental data are likely to be biased and because experiments, in principle, provide a sound basis for causal inference. But even experiments cannot overcome certain threats to inference that arise chiefly or exclusively in the context of mediation analysis-threats that have received little attention in psychology. The authors describe 3 of these threats and suggest ways to improve the exposition and design of mediation tests. Their conclusion is that inference about mediators is far more difficult than previous research suggests and is best tackled by an experimental research program that is specifically designed to address the challenges of mediation analysis.

A n enduring concern about democracies is that citizens conform too readily to the policy views of elites in their own parties, even to the point of ignoring other information about the policies in question. This article presents two experiments that undermine this concern, at least under one important condition. People rarely possess even a modicum of information about policies; but when they do, their attitudes seem to be affected at least as much by that information as by cues from party elites. The experiments also measure the extent to which people think about policy. Contrary to many accounts, they suggest that party cues do not inhibit such thinking. This is not cause for unbridled optimism about citizens' ability to make good decisions, but it is reason to be more sanguine about their ability to use information about policy when they have it.

Partisanship seems to affect factual beliefs about politics. For example, Republicans are more likely than Democrats to say that the deficit rose during the Clinton administration; Democrats are more likely to say that inflation rose under Reagan. What remains unclear is whether such patterns reflect differing beliefs among partisans or instead reflect a desire to praise one party or criticize another. To shed light on this question, we present a model of survey response in the presence of partisan cheerleading and payments for correct and "don't know" responses. We design two experiments based on the model's implications. The experiments show that small payments for correct and "don't know" answers sharply diminish the gap between Democrats and Republicans in responses to "partisan" factual questions. Our conclusion is that the apparent gulf in factual beliefs between members of different parties may be more illusory than real. The experiments also bolster and extend a major finding about political knowledge in America: like others, we show that Americans have limited knowledge about political facts, but we also show that many Americans recognize their own lack of knowledge.

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The question of how causal effects are transmitted is fascinating and inevitably arises whenever experiments are presented. Social scientists cannot be faulted for taking a lively interest in “mediation,” the process by which causal influences are transmitted. However, social scientists frequently underestimate the difficulty of establishing causal pathways in a rigorous empirical manner. We argue that the statistical methods currently used to study mediation are flawed and that even sophisticated experimental designs cannot speak to questions of mediation without the aid of strong assumptions. The study of mediation is more demanding than most social scientists suppose and requires not one experimental study but rather an extensive program of experimental research.