Keep track of when you change your mind about important facts based on new evidence.
a) If you rarely change your mind, you're probably not rational.
b) If you always change your mind, you're probably not very smart.
c) If you sometimes change your mind, and sometimes not, I think that's a pretty good indication that you're rational.
Of course, I feel that I fall into category (c), which is my own bias. I could test this, if there was a database of how often other people had changed their mind, cross-referenced with IQ.
Here's some examples from my own past...
The most important thing for me, is the near-far bias - even though that's a relatively recent "discovery" here, it still resonates very well with why I argue with people about things, and why people who I respect argue with each other.
Most frequently useful - that my interest in being unbiased can become a sort of bias of its own, when I hear arguments from others, I can easily spot the biases, and I've worked hard to recognize that I have built-in biases as well that I can't discount.
Another test.
Find out the general ideological biases of the test subject
Find two studies, one (Study A) that supports the ideological biases of the test subject, but is methodologically flawed. The other (Study B) refutes the ideological biases of the subject, but is methodologically sound.
Have the subject read/research information about the studies, and then ask them which study is more correct.
If you randomize this a bit (sometimes the study is both correct and "inline with one's bias") and run this multiple times on a person, yo... (read more)