Popular Science announced this week they are not allowing comments on their stories because “comments can be bad for science”:

But even a fractious minority wields enough power to skew a reader’s perception of a story, recent research suggests. In one study led by University of Wisconsin-Madison professor Dominique Brossard, 1,183 Americans read a fake blog post on nanotechnology and revealed in survey questions how they felt about the subject (are they wary of the benefits or supportive?). Then, through a randomly assigned condition, they read either epithet- and insult-laden comments (“If you don’t see the benefits of using nanotechnology in these kinds of products, you’re an idiot” ) or civil comments. The results, as Brossard and coauthor Dietram A. Scheufele wrote in a New York Times op-ed:

Uncivil comments not only polarized readers, but they often changed a participant’s interpretation of the news story itself.

In the civil group, those who initially did or did not support the technology — whom we identified with preliminary survey questions — continued to feel the same way after reading the comments. Those exposed to rude comments, however, ended up with a much more polarized understanding of the risks connected with the technology.

Simply including an ad hominem attack in a reader comment was enough to make study participants think the downside of the reported technology was greater than they’d previously thought.

Another, similarly designed study found that just firmly worded (but not uncivil) disagreements between commenters impacted readers’ perception of science…

A politically motivated, decades-long war on expertise has eroded the popular consensus on a wide variety of scientifically validated topics. Everything, from evolution to the origins of climate change, is mistakenly up for grabs again. Scientific certainty is just another thing for two people to “debate” on television. And because comments sections tend to be a grotesque reflection of the media culture surrounding them, the cynical work of undermining bedrock scientific doctrine is now being done beneath our own stories, within a website devoted to championing science.

In addition to rude comments and ad hominem attacks leading to changed perceptions about scientific findings, here are two common misunderstandings of how science works often found in online comments (these are also common misconceptions offline):

1. Internet conversations are ripe for argument by anecdote. This happens all the time: a study is described and then the comments are full of people saying that the study doesn’t apply to them or someone they know. Providing a single counterfactual usually says very little and scientific studies are often designed to be as generalizable as they can be. Think of jokes made about global warming: just because there is one blizzard or one cold season doesn’t necessarily invalidate a general trend upward for temperatures.

2. Argument by anecdote is related to a misconception about scientific studies: the findings do not often apply to 100% of cases. Scientific findings are probabilistic, meaning there is some room for error (this does not mean science doesn’t tell us anything – it means it is hard to measure and analyze the real world – and scientists try to limit error as much as possible). Thus, scientists tend to talk in terms of relationships being more or less likely. This tends to get lost in news stories that suggest 100% causal relationships.

In other words, in order to have online conversations about science, you have to have readers who know the basics of scientific studies. I’m not sure my two points above are necessarily taught before college but I know I cover these ideas in both Statistics and Research Methods courses.