Since mbti essentially neuters it's own usefulness in the "round those percentages down to binary" stage, you could end up with a situation where an INTP and an ESFJ have only an 8% total difference in mbti-measured personality between them.

The question isn't whether people who are in the middle of each criteria exist and could easily swap classifications to their polar opposite. The question is what percentage of people would do that and whether it's high enough that there's too little signal to noise to extract any meaningful information out of the classification system.

Don't invert the burden of proof. It's up to the proponents of MBTI to demonstrate its effectiveness.

As for signal-to-noise, mbti is a useful tool for measuring the traits it measures, it just, for some reason, cuts the signal in half by removing the percentage from the label.

Without the percentages, you can never assume a persons traits don't hover at that middle ground. And thus, can never assume any part of their label is accurate.

If the occurrence of these hover cases were more like <4%, I'd be more inclined to agree with its usefulness, but as it is right now, the 4bit label, on its own, is just noise.

i'm pretty sure someone who has gotten INTP every single test in his life will behave differently on average than someone who has always gotten ESFJ

I think its a mildly useful categorization which allows a simpler and more coarse view of personality than the full spectrum of data would normally allow.

If I ask you what your weight and height is today, it's indicative of what your weight and height will be a year from now even if the number doesn't fit into exactly the same rounded range. Doesn't mean weight and height are meaningless if the answers change classifications a bit.

A much better analogy would be blood sugar level. For many healthy people its sorta constant-ish. The fact that its not nearly constant for a subset of people doesn't prove the test is therefore worthless. It just proves some people have untreated diabetes. The test is not worthless because it can be used in diabetes screenings, unless the point of the test was to tap people like maple syrup trees or something really weird like that.

A major problem with the test is we know people are not terribly good at self introspection, we're all above average drivers and lovers and thinkers, all of us. I am good enough at self introspection to tell I'm pretty well introverted, yet I can imagine someone not so observant or self aware or perhaps neurotic about the whole topic, getting a fairly random score. Or I'm bad enough at self introspection to not realize I'm no good at it at all, and I'm actually a closet extrovert, although I find that rather unlikely (although I would, wouldn't I, if I failed at introspection).

In that way as a secondary measurement I'd propose theoretically that the wider the variation in test results, the worse the person would score in some kind of self introspection ability test. It seems a reasonable hypothesis. You'd need correction factors to deal with people having diagnosed or undiagnosed swings in brain neurotransmitters or use of addictive substances (including sugar and caffeine). But it could be run as a study.

That said there are other criticisms, for instance: Are thinking and feeling really an axis or are they two independent traits? Are there other useful axes not included?

While I sort of cringe at the idea of using this for assigning people jobs, there area few people in my life that fit some of the type narratives fairly well and it helped me understand their motivations a bit better, which did legitimately help my relationships with them.

That doesn't seem like the proper question. Specifically, it works only to predict future MBTI results, not anything further. That's fine for height and weight because those values are robust to small/moderate changes in value.

MBTI already has low predictive power about real-world content, and high sensitivity to change (on the margins; it also suffers from applying a clustered model to non-clustered data). So if retest reliability is anything less than excellent, I worry that our predictive power has been almost totally destroyed.

To provide a new analogy, this is like variance in number of fingers. The significance of 11 vs 10 vs 9 isn't proportional to magnitude, so we wouldn't accept "small" counting errors.

None of that says that "I'm an INTP" is meaningless, but I suspect that MBTI is no better, or even worse, than non-formalized personality summaries.

(Of course, MTBI is neither accurate nor precise. It is not accurate because it does not provide us any useful information about personality. It is not precise because test results vary wildly.)

Of course not. All the companies are simply wrong. They're falling for management/hiring fads, or relying on old superstitions. This happens all the time. "Companies are using it" says nothing about whether it's actually reliable.

Specifically, many studies and meta-studies have failed to show correlation between MBTI results and job performance. Here is one such summary: http://www.opd.net/abstracts5.html

Furthermore, your willingness to buy into the narrative (and others' willingness to also believe it) that by categorizing certain people into stereotypes and assuming that most of these people tend to excel at a particular set of tasks is most likely what limits them from excelling at tasks that lie outside of their respective sets just as much as their true predisposition to not excelling at them.

Saying that any profiling technique has zero predictive value is a very bold claim.

Even one's astrological sign has predictive value: [1]. And yes, this has been scientifically proven.

[1] http://www.medicaldaily.com/how-birth-month-influences-perso...

For example, companies fruitfully extract predictive power from whether a user clicked a link or not. Facebook extracts predictive power from whether users like videos, et cetera. So why shouldn't an elaborate test that was developed to have meaning, not have any predictive power?

There are results that show MBTI has no predictive power against job performance. It has not been tested against any other measure.

That said, MBTI shows bad orthogonality in the factors in its response. This suggests the factors are ill defined.

Could you provide a reference?

Does this have predictive power? Yes. If I needed somebody to take care of small children, would this test be useful? Yes of course. If I had to pick people blindly for this task, except for the results of this test, then this test would be very useful. Now, MBTI is more sophisticated than this simple test. So to say that it has no predictive power is just silly.

I'm saying that the fact that some people are using it for some purpose doesn't mean that it's actually useful for that purpose.

As for your response, the burden of proof really lies with its proponents - is there any proof of its alleged predictive power?

Without this, I don't think it's reasonable to assume that it is in fact predictive.

For example, the simple test of whether a user clicks a certain link or not already has predicitive power (companies are using this, fruitfully). So a more sophisticated test like MBTI certainly has some predictive power.

[1] https://en.wikipedia.org/wiki/Phrenology

Additionally, the added (relative) complexity doesn't imply anything about its qualities.

This is a null argument.

Unless you show that those predictions actually assess whether someone is fit for those tasks this is absolutely content free.

MBTI is a subjective categorization. Astrology is more like your DNA. You're born with a specific set pattern. Just like we don't understand what most of our genetic patterns mean, we don't understand what most of our astrological patterns mean.

http://www.nytimes.com/2015/03/08/magazine/is-most-of-our-dn...