I wonder what role the type of ailment plays in these effects. Are people perhaps more likely to use these types of remedies (even in the face of failure) when faced with an incurable disease? I expect this might be the case, as doing so might give them an illusion of control over the outcome of their illness (which they may not actually be able to control). I think this is a really interesting project and think you could explore any number of interesting moderators. I would also think about the role that illusion of control might play here. It may be an alternative explanation to rule out (since you're seeing failures attributed to the self, it may not be going on, but it would be interesting to test.