Skeptic or denier?

In my earlier post about lying with statistics, I mentioned scientific skeptics. Part of what I was thinking of was a recent (30 June 2007) edition of The Science Show about climate change (again), which included comments by Ian Plimer, which is documented in more detail in a following In Conversation episode (5 July 2007). It looks like climate is also on the agenda for this week's episode, which I haven't listened to yet.

Also saw a recent TED talk by economist Emily Oster about AIDS in Africa that challenges a lot of ideas about the disease.

That got me thinking about what's the difference between a researcher taking a minority view compared to someone who is just in denial? Who's a thoughtful doubting scientist who is thinking seriously about evidence versus someone the flat earther? (Setting myself up for hate mail from the flat earthers... yes, there really are still people out there who believe the earth is flat.)

I think there are a few guidelines.

First, is the skeptic willing to admit that he or she could be wrong? What would it take to convince you that you are wrong? If you're concerned about evidence, what evidence do you want? Is there an experiment you'd suggest should be done? What numbers do you need to see? (Plimer, for instance, expresses doubt that humans are causing climate change, but he doesn't really say what he get him to be convinced. Is there anything that would convince him or not? I don't know.)

Second, is the skeptic actually doing active research on the topic? It's one thing to read a lot of papers. Reading a lot of papers is surely important. Nevertheless, it's another to actually do it. And when you look at a lot of cases of prominent scientists who take minority views, they are often on matters outside their actual research. Lynn Margulis and Kary Mullis, for instance, are both well known scientists who expressed doubt that HIV causes AIDS, but neither of them practising virologists or epidemiologists.

And of course, the third is just how small is that minority view? This one is often really hard for outsiders to judge, particularly because media coverage is notorious for presenting opposing views as though each has equal claim to legitimacy. Someone sees a show with one person saying X and the other saying Y. There's often no easy way to tell if position X is pretty much subscribed to by researchers in every university in every country of the world who are funded through competitive grants, while position Y is backed by advocates numbering in the single digits who are backed by a private foundation.