Select Page

I love Australian Rules Football. It is one of the rare games where you can knock over a player without the ball, which makes it exciting and chaotic.

Of course choosing when you should try to tackle the player with the ball or go for the big hit on another opponent is an important one.

This is the same in debates. Its usually best to ‘play the ball’ by discussing the topic at hand but anyone that has been on social media has seen debates degenerate into full blown personal attacks, something that is often called an ad hominem attack, or ‘playing the man’.

But do these work? Well, insults are probably unlikely to get you anywhere, but Barnes et al. (2018) recently showed that claiming someone has a conflict of interest does seriously affect people’s thinking.

In fact it is more effective than debating the topic itself and is just as effective as saying someone has engaged in misconduct, such as fraud.

This obviously has some ethical considerations. I’m not suggesting people should use ad hominem attacks to discredit people who are presenting factually accurate information. However, it is important to realise that many people do exactly that, often with resounding success. For example, 91 per cent of anti-vaccine websites say that vaccine research is compromised because of conflicts of interest.

There are probably two interrelated factors at play here. Firstly, not many people know what a conflict of interest is. A conflict of interest is not collusion or corruption. And it is not evidence of bias. It is simply an acknowledgement that a professional action may be influenced by a personal interest.

Conflicts of interest may raise a red flag to the reader but they certainly don’t mean the information isn’t correct. For example, just because someone worked for the nuclear power industry, it doesn’t mean that any information they pass on about the effectiveness of wind power is wrong, it just means you might want to more verify the information more carefully than otherwise, just in case.

Secondly these conflicts of interest attacks can feed into a common conspiratorial worldview that powerful and wealthy people can pay people to produce evidence of anything that suits them. It is highly likely that these kinds of attacks would help to

In any case, don’t ignore suggestions of conflicts of interest – they might seem spurious but they’ll damage your reputation.


  • Barnes R.M., Johnston H.M., MacKenzie N., et al. (2018) The effect of ad hominem attacks on the evaluation of claims promoted by scientists. PLOS ONE 13: e0192025.
  • Wolfe R. M., Sharp L. K., & Lipsky M. S. (2002). Content and design attributes of antivaccination web sites. Journal of the American Medical Association, 287(24), 3245–3248. 287.24.3245 PMID: 12076221