Who Do You Trust?

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There are no shortages of controversial science, nutritional research, and nuclear power come readily to mind. Moreover, the down and dirty details of research in most science are directed at like-minded scientists; for the general public, sophisticated or not, details and the “truth” of the findings are above “their pay grade.” For the public to understand science, they rely on trusted intermediaries, like the American Council on Science and Health, a particular blog, or mainstream media.

For many of us, the credibility of our source becomes an important driver in the truthfulness we assign to a given piece of scientific research. Prior research suggests that we based our trust in outside sources on the sources “ability, benevolence, and integrity.”

“Respectively, these components require that the person given trust A) has the aptitude and experience to fulfill the trust, B) has a desire to fulfill the trust, and C) adheres to a set of acceptable moral principles.”

A new study in PLOS One looks at what type of attacks reduce our trust in a scientific report. More specifically, which was more effective, a factual criticism of a study’s conclusion or an ad hominem attack on its authors, e.g., misconduct, scientific incompetence, or conflict of interest. Ad hominem attacks tear at the credibility, the trust we should place, in the source information.

The researchers look at two groups, the “white-rat” of these type of studies, college students enrolled in psychology courses as well as a more diverse group of older adults. Each survey contained 12 scientific reports, six given in isolation, the remaining six associated with factual, or ad hominem attacks on the scientists, or both. Here is an example.



The results were the same for both the students and the more diverse adults. Age, gender, level of education, knowledge, and income did not affect how attacks impacted the perceived truthfulness of the claims. The education attainment and graduate education institution of researchers and their lack of attention to detail (sloppiness) did have a small impact.

We should be happy to note that attacks on the facts (empirical claims) were far more effective in moving the trust needle, but not as effective as those ad hominem attacks.



The researchers characterized the effect as moderate; the veracity scale had a six-point range, so empirical evidence moved the needle by about 8%, past misconduct about 16%. The researchers were surprised; the facts lead them to different conclusions than their initial hypothesis.

  • Ad hominem attacks are as effective as attacks on the empirical basis for a study’s findings.
  • Combining ad hominem attacks with an empirical attack was not additive.
  • Attacks on motivation, e.g., conflict of interest and misconduct, were far more effective than attacks on ability. Intent, at least in this instance, is more concerning than ability.

Most scientists would agree that ability and relevant misconduct plays a role in the credibility of scientific research. But the public, and by extension policymakers, weight conflicts of interest and past misconduct to the same degree. It raises two more profound questions with more ambiguous answers. First, what is the statute of limitations on bad deeds? Second, what constitutes a conflict of interest? Both of those questions ponder intent, and who really knows “what evil lies in the heart of men?”

[1] The Shadow, was a pulp fiction classic of the 30’s serialized on radio, comics and pulp novels. His ability to "to cloud men's minds so they cannot see him” may reflect the role of conflict of interest accusations clouding our view of scientific reports. 


Source: The effect of ad hominem attacks on the evaluation of claims promoted by scientists PLOS One DOI:10.1371/journal.pone.0192025