Mary - i allmost become sorry that i gave the example of jehovahs witnesses (but it was to tempting, given Alices recent ... i dont know what happened during the last 4 pages of that thread ... you dont have her lying in your backyard by any chance?), because its so damn obvious jehovahs witnesses are irrational most of the time they are faced with critical information. I think the effect i describe above is most relevant in non-cult religious groups and political/economical contexts.
I think it may explain a lot regarding conspiracy theories where otherwise intelligent people suddenly seem to draw the opposite conclusions on the same information; ie. a definite study which showed in great detail how a fire could have brought down the buildings can be interpreted as a non-conspiracy theorist as evidence AGAINST A conspiracy, while at the same time, the conspiracy theorists can, rationally, use it to SUPPORT there was a conspiracy.
If you are interested, i would suggest the following study:
http://www.psych.umn.edu/courses/spring07/borgidae/psy5202/readings/lord,%20ross%20&%20lepper%20(1979).pdf
Its a classical study where participants read about two studies, one concluded that the death penalty deters crime and another concluded that the death penalty has no effect on crime. After exposure to the evidence, supporters of the death penalty strengthened their support and opponents strengthened their opposition.
Had you asked me a couple of years ago, i would have taken that as a clear evidence at least one side was not being rational, but it need not be so.
A thing i left out from the original post was how to test if its irrationality or rationality which drive the other person. One simple test is to ask the person before the information is being presented what he would conclude given the information and its logical negation. For example, while Alices response to the study may have been rational in the above context, she could not the next day read a study with the opposite conclusion - that jehovahs witnesses have less pedophelia than others - and conclude that proove they are gods organization. Its one or the other, not both.
Another thing is if a person is willing to listen... but thats completely out of the scope of this post.