Derek Powell

Countering antivaccination attitudes.

Significance Myths about the safety of vaccinations have led to a decline in vaccination rates and the reemergence of measles in the United States, calling for effective provaccine messages to curb this dangerous trend. Prior research on vaccine attitude change suggests that it is difficult to persuade vaccination skeptics and that direct attempts to do so can even backfire. Here, we successfully countered people’s antivaccination attitudes by making them appreciate the consequences of failing to vaccinate their children (using information provided by the Centers for Disease Control and Prevention). This intervention outperformed another that aimed to undermine widespread vaccination myths. Three times as many cases of measles were reported in the United States in 2014 as in 2013. The reemergence of measles has been linked to a dangerous trend: parents refusing vaccinations for their children. Efforts have been made to counter people’s antivaccination attitudes by providing scientific evidence refuting vaccination myths, but these interventions have proven ineffective. This study shows that highlighting factual information about the dangers of communicable diseases can positively impact people’s attitudes to vaccination. This method outperformed alternative interventions aimed at undercutting vaccination myths.

Marginally Significant Effects as Evidence for Hypotheses Changing Attitudes Over Four Decades

Some effects are statistically significant. Other effects do not reach the threshold of statistical significance and are sometimes described as “marginally significant” or as “approaching significance.” Although the concept of marginal significance is widely deployed in academic psychology, there has been very little systematic examination of psychologists’ attitudes toward these effects. Here, we report an observational study in which we investigated psychologists’ attitudes concerning marginal significance by examining their language in over 1,500 articles published in top-tier cognitive, developmental, and social psychology journals. We observed a large change over the course of four decades in psychologists’ tendency to describe a p value as marginally significant, and overall rates of use appear to differ across subfields. We discuss possible explanations for these findings, as well as their implications for psychological research.

How Large Is the Role of Emotion in Judgments of Moral Dilemmas

Moral dilemmas often pose dramatic and gut-wrenching emotional choices. It is now widely accepted that emotions are not simply experienced alongside people’s judgments about moral dilemmas, but that our affective processes play a central role in determining those judgments. However, much of the evidence purporting to demonstrate the connection between people’s emotional responses and their judgments about moral dilemmas has recently been called into question. In the present studies, we reexamined the role of emotion in people’s judgments about moral dilemmas using a validated self-report measure of emotion. We measured participants’ specific emotional responses to moral dilemmas and, although we found that moral dilemmas evoked strong emotional responses, we found that these responses were only weakly correlated with participants’ moral judgments. We argue that the purportedly strong connection between emotion and judgments of moral dilemmas may have been overestimated.

A Single Counterexample Leads to Moral Belief Revision

What kind of evidence will lead people to revise their moral beliefs? Moral beliefs are often strongly held convictions, and existing research has shown that morality is rooted in emotion and socialization rather than deliberative reasoning. In addition, more general issues-such as confirmation bias-further impede coherent belief revision. Here, we explored a unique means for inducing belief revision. In two experiments, participants considered a moral dilemma in which an overwhelming majority of people judged that it was inappropriate to take action to maximize utility. Their judgments contradicted a utilitarian principle they otherwise strongly endorsed. Exposure to this scenario led participants to revise their belief in the utilitarian principle, and this revision persisted over several hours. This method provides a new avenue for inducing belief revision.

The Love of Large Numbers: A Popularity Bias in Consumer Choice:

Social learning—the ability to learn from observing the decisions of other people and the outcomes of those decisions—is fundamental to human evolutionary and cultural success. The Internet now provides social evidence on an unprecedented scale. However, properly utilizing this evidence requires a capacity for statistical inference. We examined how people’s interpretation of online review scores is influenced by the numbers of reviews—a potential indicator both of an item’s popularity and of the precision of the average review score. Our task was designed to pit statistical information against social information. We modeled the behavior of an “intuitive statistician” using empirical prior information from millions of reviews posted on Amazon.com and then compared the model’s predictions with the behavior of experimental participants. Under certain conditions, people preferred a product with more reviews to one with fewer reviews even though the statistical model indicated that the latter was likely to be of higher quality than the former. Overall, participants’ judgments suggested that they failed to make meaningful statistical inferences.

Reply to Betsch et al.: Highlighting risks of diseases shifts vaccine attitudes

Betsch et al. (1) argue that our intervention failed to affect “true” vaccine skeptics’ attitudes, and that the findings of our paper (2) actually support the use of an intervention aimed at dispelling myths linking measles, mumps, and rubella (MMR) vaccines and autism.

Moral Severity is Represented as a Domain-General Magnitude

The severity of moral violations can vary by degree. For instance, although both are immoral, murder is a more severe violation than lying. Though this point is well established in Ethics and the law, relatively little research has been directed at examining how moral severity is represented psychologically. Most prominent moral psychological theories are aimed at explaining first-order moral judgments and are silent on second-order metaethical judgments, such as comparisons of severity. Here, the relative severity of 20 moral violations was established in a preliminary study. Then, a second group of participants were asked to decide which of two moral violations was more severe for all possible combinations of these 20 violations. Participant’s response times exhibited two signatures of domain-general magnitude comparisons: we observed both a distance effect and a semantic congruity effect. These findings suggest that moral severity is represented in a similar fashion as other continuous magnitudes.

Array training in a categorization task

Two components of categorization, within-category commonalities and between-category distinctiveness, were investigated in a categorization task. Subjects learned three prototype categories composed of moderately high distortions, by observing arrays containing patterns that belonged either to a common prototype category or to three different categories; a third group learned patterns presented one at a time, mirroring the standard paradigm. Following 6 learning blocks, subjects transferred to old patterns and new patterns at low-, medium-, and high-level distortions of the category prototype. The results showed that array training facilitated learning, especially when patterns in the array belonged to the same category. Transfer results showed a strong gradient effect across pattern distortion level for all conditions, with the highest performance obtained following array training on different category patterns and worst in the control condition. Interestingly, the old training patterns were classified worse than new low and no better than medium distortions. Neither this ordering nor the steepness of the gradient across prototype similarity for each condition could be predicted by the generalized context model. A prototype model better captured the steep gradient and ordinal pattern of results, although the overall fits were only slightly better than the exemplar model. The crucial role played by category commonalities and distinctiveness on categorical representations is addressed.