Sorry, I'm speaking a DSL I guess. I'm talking about the difference between a prespecified analysis (one that is planned in advance) and an analysis that was no

Sorry, I'm speaking a DSL I guess. I'm talking about the difference between a prespecified analysis (one that is planned in advance) and an analysis that was not planned in advance. One of the problem with analyses that are not planned in advance is that they suffer from the problems inherent in multiple testing. If I plan in advance to compare people weighing over 150 pounds to people weighing under 150 pounds, then I am conducting one test on the data. If I, instead, collect a bunch of data and run it through the ringer, torturing it until it spits out an answer that looks good to me, then I can find all kinds of spurious associations. They are more useful for hypothesis generation (i.e., generating a hypothesis that can be tested with other data). The Wikipedia article does a better job of explaining this than I have: http://en.wikipedia.org/wiki/Post-hoc_analysis http://en.wikipedia.org/wiki/Post-hoc_analysis