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There are too many tests falling in this category which are just plain crap. However I think the Myers-Briggs test stands out from this pile of crap (eg. the daily bullshit of "what kind of animal would I like to be") since the authors have made serious effort to really measure something.
If you look at the referred wikipedia page, you will find this:
... studies have found strong support for construct validity, internal consistency, and test-retest reliability, although variation was observed.
And of course you can test it yourself (at least to some extent): just fill in the test found somewhere by google, write down your results (and even your answers to the questions) then forget it. Pick a suitable timeframe (eg. half a year), just make sure you will forget what have you answered the first time, and fill it in a second time. Then ask yourself: Are the results differing from the first time? Which ones differ? The ones that made you hesitate to answer? And so on... (extend your scope of investigation)
After all of this you're probably still inclined to ask: okay it seems to measure something, but what it is?
And for that I don't have a good answer. For instance if I have to measure time (eg. while I finished some of my work) and I follow some procedure (take a stopper watch, start the counter when I started then stop it when I stopped), then do I need to answer the question "What is time?" to be able to use this measurement?
At the end of the day what I want to say is: "psychological measurment is not possible" is not a consequence of "there are gazillions of shitty psychobabble tests". And also not a consequence of "I can cheat while filling in the test".
And I think the Myers-Briggs test is a good candidate of being not shitty.
p.s.: Seeing the results up to now (almost half of the voters chose "I Don't Friggin Care"), I think I will get a lot of negative votes for this node, but I Don't Friggin Care. Reject anything if you want but based on investigation and not on ignorance.
p.p.s.: This answer is not really meant to you, but all the voters of IDFC.
In reply to Re^2: My Myers-Briggs Personality Type Indicator is ...