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FAMILY gatherings can bring up contentious topics we prefer to avoid, and with the festive season in full swing, it might be hard to dodge your more science-averse relatives. At some point, you know they will start spouting falsities, such as: 鈥淗IV doesn鈥檛 cause AIDS鈥�, 鈥淕enetically modified foods are not safe to eat鈥�, 鈥淐limate change is a conspiracy鈥� or 鈥淰accines cause autism鈥�. (Again, all these statements are untrue.)

If this happens, you don鈥檛 have to just sit there quietly fuming. 鈥淚s it worth making an effort to correct people?鈥� says Jason Reifler at the University of Exeter, UK, who studies ways of challenging misperceptions. 鈥淚 think so.鈥�

Obviously, it is inherently more difficult to refute false beliefs than to spread them. Anyone can parrot a lie, but it usually takes a bit of time and knowledge to explain why a statement is wrong.

Take a classic: 鈥淭he climate has always changed, it鈥檚 nothing to do with humans.鈥� To counter this, you need to explain how the world is now warming at an unprecedented rate, when otherwise it would be cooling slightly were it not for our carbon dioxide emissions. If you don鈥檛 know the specifics, there are websites such as that debunk common myths.

鈥淎nyone can parrot a lie, but it usually takes a bit of time and knowledge to explain why a statement is wrong鈥�

But sometimes there are shortcuts to make your point convincing. 鈥淧arallel鈥� arguments can often highlight logical flaws very effectively, says John Cook of George Mason University, Virginia, who set up Skeptical Science after arguing with his father-in-law. For instance, the 鈥渃limate is always changing鈥� myth is like claiming that because people have always stolen from each other, leaving your house unlocked won鈥檛 up the risk of burglary.

But you need to beware the backfire effect. This is the idea that trying to change someone鈥檚 false belief can make them believe it more strongly. It a decade ago when Reifler and a colleague looked at why people continued to believe that Iraqi dictator Saddam Hussein had weapons of mass destruction, despite none ever being found. When they tried to correct this belief in a group of people, they found that these efforts .

This was discouraging news for the fight against false beliefs. 鈥淭he last thing you want to do when debunking misinformation is blunder in and make matters worse,鈥� wrote Cook and Stephan Lewandowsky at the University of Bristol, UK, in , a short guide published in 2011.

However, more recent studies are far more encouraging. 鈥淚t鈥檚 not as prevalent as we initially thought,鈥� says Lewandowsky.

In the handbook, he and Cook looked at three types of backfire effect. The simplest is the 鈥渙verkill鈥� effect, the idea that if you bombard people with too many counterarguments, they can鈥檛 process all the information and end up believing the false facts more strongly.

But in a , a team including Lewandowsky found that using four to six counterarguments led to at least as much belief reduction as using just two. 鈥淚 think the overkill backfire effect is only an issue if you are using poor arguments,鈥� says lead author Ullrich Ecker at the University of Western Australia in Perth.

What does this mean for family arguments? If you are not sure of the facts, do some surreptitious web browsing on your phone rather than trying to wing it.

Truth sandwich

The second type is the familiarity backfire effect, the idea that just talking about a myth can reinforce belief. This led to some rather tricky advice: try to avoid repeating myths when refuting them. But again, recent studies don鈥檛 back this up.

Still, if someone isn鈥檛 paying attention, they could be left with the wrong idea. Suppose you are reeling off evidence that there is no link between vaccination and autism, such as the fact that the incidence of autism rose in Japan even when the MMR vaccine was temporarily withdrawn. If a bystander who has never heard of the issue catches only snippets of the conversation, they might end up with the false impression that there is a link.

So it is still safest to present a 鈥渇actual wrapper鈥� or 鈥渢ruth sandwich鈥�: start with the facts before mentioning the myth, then repeat the facts. You can see this in action around the falsehoods at the top of this article.

Then there鈥檚 the world-view backfire effect, the notion that if a correction clashes with your world view, it strengthens the misconception. Reifler , but he points out that the effect only appeared in two out of five experiments.

What鈥檚 more, although , . This suggests it is much rarer than Reifler鈥檚 work suggested, which he thinks is fantastic news.

So why the conflicting results? We don鈥檛 know, but some people might be especially susceptible. According to one , belief in fake news is associated with 鈥渄elusionality, dogmatism, religious fundamentalism, and reduced analytic thinking鈥�.

But whatever you do, don鈥檛 point this out, or resort to outright confrontation or insults (鈥淵ou鈥檙e wrong!鈥�, 鈥淵ou鈥檙e ignorant鈥�.). Instead, listen and ask questions that reveal why someone has those opinions (鈥淲hat makes you think that?鈥�).

鈥淩espect the fact that they may have had experiences that led them to believe what they believe,鈥� says Ecker.

The good news is that social events are excellent situations for refuting myths. Assuming there is at least some trust between you, the other person will probably hear you out, says Ecker. And corrections from credible, trusted sources are more effective. There鈥檚 also far more time to discuss the topic in person than compared with, say, interactions on social media.

The bad news is that even with all this in mind, you are still unlikely to convince someone, especially if you are challenging their world view. 鈥淲orld view-dissonant corrections are by-and-large ineffective, especially in conservative people,鈥� says Ecker. 鈥淭hat doesn鈥檛 mean that liberal people are immune to world-view effects, but I have only seen total lack of efficacy in conservative people.鈥�

So why even try? Firstly, people are much less likely to spread false information if they are held accountable for it, says Reifler. Questioning your relatives鈥� false claims may make them think twice before spouting nonsense on another occasion.

And always consider the other people in the room. 鈥淓ven if you do not change your Aunt Susan鈥檚 mind, you may sow a seed in your nieces鈥� and nephews鈥� minds,鈥� says Ecker.

鈥淎round 300,000 people died in South Africa because of denialism about HIV and AIDS鈥�

Indeed, Cook thinks there is little chance of changing the minds of, say, the who are very sure that global warming isn鈥檛 happening at all. Instead, he thinks we should focus on the majority still open to persuasion. His studies show that for false arguments if they are 鈥渋noculated鈥� against them.

For instance, forewarn them about the problem of false balance in the media 鈥� where commentators with no expertise are interviewed just to give an opposing position 鈥� and their views won鈥檛 change when they read an article full of false-balance quotes. Those who are not warned become more doubtful.

So when you tell Aunt Susan that her incorrect views on climate science are the result of deliberate efforts to muddy the truth and thwart action, she might not believe you. But inoculating her children might stop them falling for climate change deniers鈥� propaganda.

If all this seems discouraging, remember that the truth matters. Children are dying because of the . It is estimated that because of denialism about HIV and AIDS.

And occasionally you might just change someone鈥檚 mind 鈥� but don鈥檛 expect any thanks. While Cook鈥檚 father-in-law remains unconvinced about climate change, his father has changed his mind. But when Cook asked him why, he encountered a phenomenon seen in some studies: his father denied ever having thought otherwise.

This article appeared in print under the headline 鈥淧ass the facts, would you?鈥�