Let me devise a test. The test is just "are you a man or a woman?".

Does this have predictive power? Yes. If I needed somebody to take care of small children, would this test be useful? Yes of course. If I had to pick people blindly for this task, except for the results of this test, then this test would be very useful. Now, MBTI is more sophisticated than this simple test. So to say that it has no predictive power is just silly.

While I'm not a huge fan of Myers-Briggs (or rather, how it's used), that's not what I'm saying.

I'm saying that the fact that some people are using it for some purpose doesn't mean that it's actually useful for that purpose.

As for your response, the burden of proof really lies with its proponents - is there any proof of its alleged predictive power?

Strictly speaking you are right, my logic was flawed (hidden assumption). But let's stick with the orignal issue here, which is whether the test is predictive.

Agreed - this is why I asked whether there is any proof of its alleged predictive power.

Without this, I don't think it's reasonable to assume that it is in fact predictive.

Yes, but the point I'm trying to make is that the claim that any test has zero predicitive power is actually pretty bold.

For example, the simple test of whether a user clicks a certain link or not already has predicitive power (companies are using this, fruitfully). So a more sophisticated test like MBTI certainly has some predictive power.

This is a completely bogus argument. Phrenology[1] on its face sounds pretty sophisticated, but it still has zero predictive power.

[1] https://en.wikipedia.org/wiki/Phrenology

Read this: http://www.medicaldaily.com/how-birth-month-influences-perso...

Unless it is demonstrated to have some predictive power, it isn't certain at all.

Additionally, the added (relative) complexity doesn't imply anything about its qualities.

According to your logic, sophistication implies better predictive power. You completely ignore the fact that someone could devise a very elaborate system for judging e.g. fitness for a certain job, make very good assumptions and work very hard and still achieve poor predictive power.

True, but not very likely.