https://en.wikipedia.org/wiki/Myers%E2%80%93Briggs_Type_Indi...
That said, I don't think it's quite true that "The MBTI is approximately as valid as the Big 5". It seems to me that the Big 5 is a strict improvement on the MBTI. First, the discrete nature of the MBTI incorrectly suggests that the distributions are bimodal, when I don't think anyone thinks that's true. Second, I'm willing to bet that even if we just concentrate on the 4 factors of the Big 5 that correlate with the (non-discrete version of the) MBTI factors, we'd find significantly higher validity for the former, if only because there have been many more serious scientists studying and refining it over many years.
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You're describing salesmanship and/or popularizing techniques, not scientific validity.
If you are a logical positivist and scientific realist you'll never be able to grok this. As a utilitarian I understand that science is the process of making something that does something you want done.
Thanks!
I'm no statistician, but "is approximately as valid" looks to be overselling the situation.
Also correlation is a linear operator which is not particularly sensitive to anything nonlinear. Use a good statistical test instead.