OVERVIEW The O.J. Simpson " trial of the century " in the mid-1990s captured the attention of the American populace more than any other public spectacle since the kidnaping of the Lindberg baby in the 1920s. A prominent football player and popular sportscaster was charged with a gruesome double homicide. The attorneys for the prosecution and defense were of various races and genders. The evidence presented on each side was at times amazingly simple, visual, and emotional, and at times was verbal, abstract, and probably incomprehensible to jurors. The witnesses included individuals of diverse styles, demeanors, and credibility. The jurors, the recipients of the messages from these various sources, were themselves a mixed group of people of diverse backgrounds, beliefs, and personal experiences who had to sift through the trial material and arrive at a decision as to whether the defendant had been proven guilty or not. The context in which all of this took place was at times tense and sad, and at times filled with humor and positive feelings. Not surprisingly, no experiment has ever captured the extraordinary complexity inherent in this situation, yet almost all of the variables present in this trial (and many not present) have been examined in the social psychological literature on attitude formation and change. This chapter provides an overview of research on these diverse variables and addresses the processes by which these variables are thought to result in influence. Although it has become a cliché to say that the attitude construct is the most indispensable concept in contemporary social psychology, this statement appears as true today as when Allport (1935) initially wrote it in reviews of the attitude concept). Attitudes remain important as we enter the 21st century because of the fundamental role that individuals' attitudes, both explicit and implicit (Greenwald & Banaji, 1995), play in the critical choices people make regarding their own health and security as well as those of their families, friends, and nations. From purchase decisions provoked by liking for a product to wars spurned by ethnic prejudices, attitudes help to determine a wide variety of potentially consequential outcomes. Before turning to the relevant studies, it is useful to address some definitional issues. The term attitude is used to refer to a person's overall evaluation of persons (including oneself), objects, and issues. Thus, one's attitude refers to how favorably or unfavorably or how positively or negatively in general …

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Attitude change: Multiple roles for persuasion variables.

Shortly after publication, Donald T. Campbell and Julian C. Stanley's "Experimental and Quasi-Experimental Designs for Research on Teaching" (1963) gained the status of a classic exposition of experimentation in education. There have been few attempts to extend this pioneering work, as might be expected of a work so comprehensive in conception and so brilliant in execution. Webb et al. (1966) produced a work similar in purposethat being to identify sources of external invalidity which arise from the reactive effect of measurement. We know of no other

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The External Validity of Experiments

Publisher Summary This chapter describes various approaches to the problem of inducing resistance to persuasion, and presents a number of variations on each approach. Persuasive messages are known to be more effective if they are presented with their conclusions explicitly drawn, rather than left to be drawn by the recipient. Several ways of inducing resistance to persuasion, and some possibly pretreatments—like enhancing the person's tendency to use perceptual distortion in the defense of his preconceptions—are included in the chapter. Some contemporary approaches to inducing resistance to persuasion include the behavioral commitment approach, anchoring the belief to other cognitions, inducing resistance cognitive states, and prior training in resting persuasive attempts. It is believed that with better education the individual becomes more resistant to persuasion. However, empirical research does not consistently support such a proposition. It is by no means clear that any general-education manipulation would have the effect of increasing resistance to persuasion. Training more specifically tailored to reduce susceptibility to persuasion might be more successful. There is some evidence that the more intelligent are more resistant to conformity pressures from peers, but they also seem to be more susceptible to the mass-media kind of persuasion attempts. Further experiments will have to determine, if inoculation theory will predict the immunizing efficacy of various types of defenses in the case of controversial beliefs as successfully as it has for truisms.

Some Contemporary Approaches

Contemporary research on attitude change processes is reviewed for implications regarding the relative influence of successive opposing messages on final judgments. Based on this review, extent of message relevant elaboration is offered as a moderator of primacy versus recency effects in prior research. Support for this view is derived from the ability to explain the results of previous studies and from two experiments in which message presentation order and personal relevance of the topic are manipulated in a factorial design. We find that situations that foster high levels of message elaboration lead to greater influence of an initial message on final judgments (a primacy effect) whereas situations that foster low levels of message relevant elaboration lead to greater influence of a second message on final judgments (a recency effect).

Message Order Effects in Persuasion: An Attitude Strength Perspective

One of the causes of the underuse of the Solomon four-group design may be that the complete details for the statistical analysis have not previously been presented. The primary issue previously unaddressed was how to combine an analysis of the effect of the treatment in the posttest-only groups with the same effect in the pre- and posttest groups (after an earlier phase of the analysis has shown no evidence of pretest sensitization.) A meta-analytic solution for this problem is proposed, and the entire analysis is presented, complete with flowchart and example. It is shown that the analysis has adequate statistical power even if the total N is not increased from that of a posttest-only design, removing the last of the serious objections to the Solomon design.

Statistical Treatment of the Solomon Four-Group Design: A Meta-Analytic Approach

Pretest-treatment interaction effects in attitudinal studies.

Three theoretical interpretations of order effects in persuasive communications.

(1960). Manipulation-Exploration Drives and the Drive Reduction Hypothesis. The Journal of General Psychology: Vol. 63, No. 1, pp. 3-27.

Robert E. Lana

Papers

Pretest-treatment interaction effects in attitudinal studies.

Three theoretical interpretations of order effects in persuasive communications.

Manipulation-Exploration Drives and the Drive Reduction Hypothesis