Reconciling MBTI with Big 5

[BlackDog]

Recent studies have confirmed that the MBTI and Big 5 are testing the same thing. So the test must be valid, right?

On the other hand, it has also been demonstrated that the dichotomies don't exist; traits fall on a bell curve.

This is interpreted to mean that the dichotomous types cannot exist.

However, note that the human mind is attuned to differences; this is what is useful to us.

Given that, what if the difference between one type and another is only a few percentage points of preference?

In other words, although objectively maybe the types have 75% overlap, making the bulk of thought processes the same, the remaining 25% is what we have to play with among different people, creating the types for all practical purposes due to the way our minds work?

So, maybe dichotomies do exist, just as exaggerated operational versions of the true differences?

This idea may be old. But I haven't heard of it until now.

 

[á´…eparted]

If two ideas that seem different are the same, it doesn't validate them; both could just as easily be wrong together.

 

[PocketFullOf]

Seems pretty logical...same with the concept if race tbh it's not a novel idea you have but it's a good one.

- - - Updated - - -

If two ideas that seem different are the same, it doesn't validate them; both could just as easily be wrong together.

Yes also this.

 

[BlackDog]

If two ideas that seem different are the same, it doesn't validate them; both could just as easily be wrong together.

There is no general theory in the humanities; all of this is just made-up cobbled together personal systems. All of it. So if something works, the only way to know it is either intuition or correlational studies. Preferably both. Big 5 has correlational studies but no intuitive basis. So if we can fuse MBTI to it, we might have a more useful system.

 

[á´…eparted]

There is no general theory in the humanities; all of this is just made-up cobbled together personal systems. All of it. So if something works, the only way to know it is either intuition or correlational studies. Preferably both. Big 5 has correlational studies but no intuitive basis. So if we can fuse MBTI to it, we might have a more useful system.

...you completely missed the point of what I just said. I'll rephrase:

Theory A states X conclusion. Theory B states Y conclusion.

Study C reveals X and Y are pretty much the same thing, therefore theory A and B are one in the same.

This speaks absolutely NOTHING of Theory A and B's accuracy, at all. Just because they produce the same result does not automatically make them correct. That's the problem with the conclusion you're drawing. I am not debating (nor am I interested in) the accuracy and validity of MBTI and other personality theories. It's boring to me. That said, stating because they produce the same result validates them is completely wrong and illogical.

 

[reckful]

The fact that the preference strengths of the MBTI dimensions exhibit something like a normal distribution — to the extent that that's true (and I think it probably is) — doesn't mean that the "dichotomies don't exist." It just means that they have a normal distribution.

And the fact that somebody's near the middle of the curve — say, a 10% T — has nothing to do with "thought processes overlapping." It just means their T preference is on the mild side.

For what it's worth, Jung thought more people were essentially in the middle on E/I than were significantly extraverted or introverted, and Myers allowed for the possibility of middleness on all four dimensions — so the in-the-middle possibility really goes all the way back to the MBTI's roots.

Myers believed that it might turn out that one or more of the dichotomies was truly bimodal to one degree or another — with, in effect, a more or less empty (if narrow) zone in the exact middle of the spectrum. But she never asserted that that theoretical possibility had been factually established by any respectable body of evidence, and the 1985 MBTI Manual (which she co-authored) stressed that the evidence for bimodality was sketchy at best. And since then, quite a lot of evidence has accumulated that seems to suggest that most or all of the MBTI dimensions exhibit something more like a normal distribution.

In at least one of the early versions of the MBTI, it was possible to get an "x" on any dimension. The current version assigns people a (tentative) type on each dimension, but that's a very different thing from saying that it isn't possible for someone not to have a preference — and the MBTI Manual specifically notes that someone with a score near the middle is someone who has essentially "split the vote" rather than offered much evidence of a preference.

The "Step II" version of the MBTI includes five "facets" for each dimension — just as the NEO-PI-R has six facets for each Big Five dimension — and allows for the possibility of being, for example, on the T side of three of the facets and the F side of the other two.

But most importantly, for purposes of this discussion: there was really no doubt in either Jung's or Myers' minds that people on either side of the dimensions fell along a notably wide spectrum from mild to strong preferences.

As a final note: At this point nobody really knows how close to the middle how many people are on the MBTI (and Big Five) dimensions, because the current state of both the MBTI and Big Five is such that it really isn't possible to determine exactly where anybody falls along whatever the real, underlying (and substantially genetic) spectrums may be. So it seems to me that anybody who thinks that the existing data on either the Big Five or MBTI has clearly established the shape of the distribution curves is very much overestimating the ability of the existing tests to accurately quantify strengths of preferences.

But the main point to keep in mind is that, at the end of the day, the worth of the MBTI and Big Five is mostly going to hinge on how good a job those typologies do in nailing down what personality-related characteristics tend to be associated with the corresponding preferences, and not on how many people turn out to be at any particular point on any of the relevant spectrums. And in any case, the MBTI certainly doesn't stand or fall depending on whether any of its dimensions exhibit a "bimodal" distribution.

 

[BlackDog]

...you completely missed the point of what I just said. I'll rephrase:

Theory A states X conclusion. Theory B states Y conclusion.

Study C reveals X and Y are pretty much the same thing, therefore theory A and B are one in the same.

This speaks absolutely NOTHING of Theory A and B's accuracy, at all. Just because they produce the same result does not automatically make them correct. That's the problem with the conclusion you're drawing. I am not debating (nor am I interested in) the accuracy and validity of MBTI and other personality theories. It's boring to me. That said, stating because they produce the same result validates them is completely wrong and illogical.

Actually, it isn't. Don't run what I am saying through a true/false program, try to understand context.

Human psychology involves far too much complexity for us to model it at this time. Any internally consistent system which we kind of feel is valid is the definition of valid at this time. If we can make approximately accurate mental estimates, then that is valid.

So yes, because they produce the same result they are validated 'more'. Validation is a process which occurs in stages in a subject as soft as this.

 

[á´…eparted]

Actually, it isn't. Don't run what I am saying through a true/false program, try to understand context.

Human psychology involves far too much complexity for us to model it at this time. Any internally consistent system which we kind of feel is valid is the definition of valid at this time. If we can make approximately accurate mental estimates, then that is valid.

So yes, because they produce the same result they are validated 'more'. Validation is a process which occurs in stages in a subject as soft as this.

...you completely missed the point again. I am not speaking of the validity of MBTI or Big 5 (I don't care). I am speaking of the conclusion pattern you are drawing.

You said:

Recent studies have confirmed that the MBTI and Big 5 are testing the same thing. So the test must be valid, right?

You spoke nothing of the validity of MBTI and Big 5. You simply stated that they result the same thing, therefore must be valid. That is illoigcal. Period. End of discussion, for the reasons I already said.

If there is solid evidence that supports MBTI and or Big 5 (such as an APA publication), then yes this increases validity of an already valid study. In the absence of this though, this does not work.

 

[BlackDog]

The fact that the preference strengths of the MBTI dimensions exhibit something like a normal distribution — to the extent that that's true (and I think it probably is) — doesn't mean that the "dichotomies don't exist." It just means that they have a normal distribution.

And the fact that somebody's near the middle of the curve — say, a 10% T — has nothing to do with "thought processes overlapping." It just means their T preference is on the mild side.

For what it's worth, Jung thought more people were essentially in the middle on E/I than were significantly extraverted or introverted, and Myers allowed for the possibility of middleness on all four dimensions — so the in-the-middle possibility really goes all the way back to the MBTI's roots.

Myers believed that it might turn out that one or more of the dichotomies was truly bimodal to one degree or another — with, in effect, a more or less empty (if narrow) zone in the exact middle of the spectrum. But she never asserted that that theoretical possibility had been factually established by any respectable body of evidence, and the 1985 MBTI Manual (which she co-authored) stressed that the evidence for bimodality was sketchy at best. And since then, quite a lot of evidence has accumulated that seems to suggest that most or all of the MBTI dimensions exhibit something more like a normal distribution.

In at least one of the early versions of the MBTI, it was possible to get an "x" on any dimension. The current version assigns people a (tentative) type on each dimension, but that's a very different thing from saying that it isn't possible for someone not to have a preference — and the MBTI Manual specifically notes that someone with a score near the middle is someone who has essentially "split the vote" rather than offered much evidence of a preference.

The "Step II" version of the MBTI includes five "facets" for each dimension — just as the NEO-PI-R has six facets for each Big Five dimension — and allows for the possibility of being, for example, on the T side of three of the facets and the F side of the other two.

But most importantly, for purposes of this discussion: there was really no doubt in either Jung's or Myers' minds that people on either side of the dimensions fell along a notably wide spectrum from mild to strong preferences.

As a final note: At this point nobody really knows how close to the middle how many people are on the MBTI (and Big Five) dimensions, because the current state of both the MBTI and Big Five is such that it really isn't possible to determine exactly where anybody falls along whatever the real, underlying (and substantially genetic) spectrums may be. So it seems to me that anybody who thinks that the existing data on either the Big Five or MBTI has clearly established the shape of the distribution curves is very much overestimating the ability of the existing tests to accurately quantify strengths of preferences.

But the main point to keep in mind is that, at the end of the day, the worth of the MBTI and Big Five is mostly going to hinge on how good a job those typologies do in nailing down what personality-related characteristics tend to be associated with the corresponding preferences, and not on how many people turn out to be at any particular point on any of the relevant spectrums. And in any case, the MBTI certainly doesn't stand or fall depending on whether any of its dimensions exhibit a "bimodal" distribution.

I think you have a hard time justifying binary mental constructs (T and F, for example) if the distribution is not bimodal. Imagine the converse, that there was a big dead zone in the middle. That would have been very strong evidence that people really do tend to fall into these two mentally constructed boxes, or else that they learned to classify their behavior (or simply learned to behave) in one of these two modes.

The only other way I could think of to justify this system is if people effectively behave, or can be treated as if they behave, bimodally.

 

[BlackDog]

...you completely missed the point again. I am not speaking of the validity of MBTI or Big 5 (I don't care). I am speaking of the conclusion pattern you are drawing.

You said:



You spoke nothing of the validity of MBTI and Big 5. You simply stated that they result the same thing, therefore must be valid. That is illoigcal. Period. End of discussion, for the reasons I already said.

If there is solid evidence that supports MBTI and or Big 5 (such as an APA publication), then yes this increases validity of an already valid study. In the absence of this though, this does not work.

Wrong. Internally consistent systems in psychology can be assumed to be automatically valid. I didn't miss your point; I disagree. If two separate internally consistent systems agree, then they are more valid. That's how it works.

 

[á´…eparted]

Wrong. Internally consistent systems in psychology can be assumed to be automatically valid. I didn't miss your point; I disagree. If two separate internally consistent systems agree, then they are more valid. That's how it works.

[MENTION=19948]Showbread[/MENTION], you're a senior in psychology. Is this how theories work? It's the first I've heard of it and I am not aware of this being the case in any other field.

 

[reckful]

I think you have a hard time justifying binary mental constructs (T and F, for example) if the distribution is not bimodal. Imagine the converse, that there was a big dead zone in the middle. That would have been very strong evidence that people really do tend to fall into these two mentally constructed boxes, or else that they learned to classify their behavior (or simply learned to behave) in one of these two modes.

The only other way I could think of to justify this system is if people effectively behave, or can be treated as if they behave, bimodally.

The fact that you can't "think of" it for some reason is just a problem at your end. None of the MBTI dimensions (or the Big Five dimensions they essentially correspond to) are well characterized as "mentally constructed boxes."

Let's say part of what an N preference involves is a tendency to be attracted to change and novelty and, conversely, part of what an S preference involves is a tendency to resist change and novelty. If somebody's got a very mild N preference, their internal tug in the direction of change and novelty is very mild. And if somebody's in the middle, they don't really have a significant tug in either direction.

There's nothing about that "binary construct" that's inconsistent with a normal distribution.

Whether some or all of the MBTI dimensions are dichotomous in the sense of, in effect, having the 0 in the middle (with opposed tendencies in each direction) is a separate issue from the shape of the distribution curve.

 

[Jaguar]

The only other way I could think of to justify this system is if people effectively behave, or can be treated as if they behave, bimodally.

People with different preferences can engage in the same behavior. Furthermore, people can behave differently depending on the context in which they find themselves. The masks people take on and off to deal with different environments (work vs home, for example), and the accompanying behavior, can be extreme.

 

[Showbread]

Wrong. Internally consistent systems in psychology can be assumed to be automatically valid. I didn't miss your point; I disagree. If two separate internally consistent systems agree, then they are more valid. That's how it works.

That's kind of how it works... The problem with the MBTI is that isn't reliable OR valid. People's results change over the course of a lifetime, or even over the course of a week depending on mood. At least as far as testing is concerned they do. People who do independent research and basically immerse themselves in it for awhile probably come to a consistent conclusion. The problem with MBTI is that even when it is reliable, it's not terribly internally consistent. It's too subjective from person to person. People define things like "abstract thought," "logical conclusions," and "compassion" differently. Because of the subjectivity, we don't know what we are actually measuring. Same can be said for Big 5, although in my experience it is held in higher esteem than MBTI by most researchers.

[MENTION=20829]Hard[/MENTION], I'm definitely tracking with your logic. Just because they match does not mean they are both correct. They could be wrong, or mis-measuring the same thing. All of my Psych professors HATE the MBTI. They don't think it's valid, or internally consistent. None of them are terribly keen on any personality inventories for the same reason.

 

[BlackDog]

The fact that you can't "think of" it for some reason is just a problem at your end. None of the MBTI dimensions (or the Big Five dimensions they essentially correspond to) are well characterized as "mentally constructed boxes."

Let's say part of what an N preference involves is a tendency to be attracted to change and novelty and, conversely, part of what an S preference involves is a tendency to resist change and novelty. If somebody's got a very mild N preference, their internal tug in the direction of change and novelty is very mild. And if somebody's in the middle, they don't really have a significant tug in either direction.

First of all, we are just asserting the existence of S and N. Period. Jung made them up as a handy way to categorize the human differences he saw in his practice. That's nice, but it isn't empirical. It's a mental shortcut that organizes our thinking.

I could make up two letters, called B and F, and say that part of a B preference is an aggressive attitude toward life, and part of an F preference is a passive attitude toward life. And I could say that another part of the B preference is a preference for loud clothing, and the converse for a part of F. And then I construct a personality test which uses a number of different items designed to test for those two things that we associated.

I just made those preferences up. I have no evidence that they 'exist' outside of my categorization system. What determines if the system is more or less valid depends on two things: In a study can I find a correlation between loud clothing and an aggressive attitude toward life, and also is there a logical construct in my system that makes sense of why the two are correlated at all?

The same is true of S and N. Sure, S and N don't need to be bimodal if you don't define them that way. You can define your system to be any way you want. But that doesn't mean it is valid.

If, on the other hand, S and N were distributed bimodally, you would have some kind of evidence that S and N are labeling the effects of some kind or cluster of real physiological differences, rather than just being arbitrary logical constructs that humans are using to categorize.

When you speak of 'mild internal tug' and 'strong internal tug', what are you really talking about? What is doing the tugging? There is no evidence that S and N are physiological; just like B and F they are mental constructs (more sophisticated logically than B and F, hence why MBTI is appealing) that organize essentially random data.

So, S and N like B and F are to be understood as description, not explanation.

There's nothing about that "binary construct" that's inconsistent with a normal distribution.

Whether some or all of the MBTI dimensions are dichotomous in the sense of, in effect, having the 0 in the middle (with opposed tendencies in each direction) is a separate issue from the shape of the distribution curve.

I disagree.

 

[reckful]

The same is true of S and N. Sure, S and N don't need to be bimodal if you don't define them that way. You can define your system to be any way you want. But that doesn't mean it is valid.

If, on the other hand, S and N were distributed bimodally, you would have some kind of evidence that S and N are labeling the effects of some kind or cluster of real physiological differences, rather than just being arbitrary logical constructs that humans are using to categorize.

There are issues where reasonable people can disagree and issues where there's a right and wrong, and this is one of the latter issues. Whether a personality dimension is capable of demonstrating psychometrically respectable "validity" and whether it's bimodal are independent issues.

As further discussed in the "Big Five is science and the MBTI is astrology" and "Real psychologists reject the MBTI" sections of this post, the dichotomy side of the MBTI can now point to decades of respectable data support, and McCrae and Costa (the leading Big Five psychologists) long ago acknowledged that the MBTI, besides effectively tapping into four of the Big Five factors, also passed muster in the reliability and validity departments.

And the Big Five dimensions also have decades of respectable support for their validity.

And that's without either the Big Five or MBTI dimensions demonstrating a bimodal distribution.

"Validity" basically has to do with whether the theoretical constructs are found to significantly correlate with real-world stuff that goes beyond the specific things that the applicable test asked the subjects about. To the extent that a personality dimension demonstrates that, it has validity, regardless of what the shape of the distribution curve (in terms of weak and strong preferences) may turn out to be.

In the spoiler are membership stats for TC and Personality Café. For each type, the first percentage is the percentage of that type at the forum, the second percentage (in parentheses) is the estimated "general population" percentage from the official MBTI folks (from this page), and the final number on the right is the self-selection ratio for that type — i.e., the ratio of the forum percentage to the general population percentage.

November 2014 membership stats for Personality Café:

INFJ — 9133 — 15.7% (1.5%) — ssr: 10.5
INTJ — 7307 — 12.6% (2.1%) — ssr: 6.0
INFP — 11865 — 20.4% (4.4%) — ssr: 4.6
INTP — 7825 — 13.5% (3.3%) — ssr: 4.1
ENTP — 3709 — 6.4% (3.2%) — ssr: 2.0
ENTJ — 1681 — 2.9% (1.8%) — ssr: 1.6
ENFJ — 1904 — 3.3% (2.5%) — ssr: 1.3
ENFP — 4915 — 8.5% (8.1%) — ssr: 1.0
ISTP — 1926 — 3.3% (5.4%) — ssr: 0.6
ISFP — 1986 — 3.4% (8.8%) — ssr: 0.4
ISTJ — 2094 — 3.6% (11.6%) — ssr: 0.3
ESTP — 635 — 1.1% (4.3%) — ssr: 0.3
ISFJ — 1374 — 2.4% (13.8%) — ssr: 0.2
ESFP — 620 — 1.1% (8.5%) — ssr: 0.1
ESFJ — 573 — 1.0% (12.3%) — ssr: 0.1
ESTJ — 542 — 0.9% (8.7%) — ssr: 0.1

November 2014 membership stats for Typology Central:

INFJ — 1782 — 16.1% (1.5%) — ssr: 10.7
INTJ — 1437 — 13.0% (2.1%) — ssr: 6.2
INTP — 1958 — 17.7% (3.3%) — ssr: 5.4
INFP — 2016 — 18.2% (4.4%) — ssr: 4.1
ENTP — 781 — 7.0% (3.2%) — ssr: 2.2
ENTJ — 298 — 2.7% (1.8%) — ssr: 1.5
ENFP — 1156 — 10.4% (8.1%) — ssr: 1.3
ENFJ — 321 — 2.9% (2.5%) — ssr: 1.2
ISTP — 304 — 2.7% (5.4%) — ssr: 0.5
ISFP — 256 — 2.3% (8.8%) — ssr: 0.3
ISTJ — 278 — 2.5% (11.6%) — ssr: 0.2
ESTP — 100 — 0.9% (4.3%) — ssr: 0.2
ISFJ — 181 — 1.6% (13.8%) — ssr: 0.1
ESFP — 84 — 0.8% (8.5%) — ssr: 0.1
ESTJ — 74 — 0.7% (8.7%) — ssr: 0.1
ESFJ — 65 — 0.6% (12.3%) — ssr: 0.05

Looking at the PerC stats (the larger sample): 62% of the members are INs (as compared to 11% of the general population), and 83% of the members are N's (as compared to 27% of the general population).

Every S type has a self-selection ratio of 0.6 or lower, and no N type has a self-selection ratio below 1.0. And the lowest self-selection ratio for the IN types is 13 times higher than the highest self-selection ratio for the ES types.

The stats suggest than an average MBTI IN is something like 40 times mores likely than an average MBTI ES to join a personality-related internet forum.

And the stats for the second forum are strikingly similar to the ones for the first.

Those typings aren't "official," but that's a non-issue for purposes of this discussion (and also really a non-issue given the magnitude of the N and I skews).

Assume for the sake of discussion that the relevant typings were all "official MBTI" typings. In that case, those would unquestionably be a strongly supportive set of results from the standpoint of the validity of the MBTI E/I and S/N dichotomies. The MBTI doesn't ask people if they use internet forums (or the internet), and it doesn't ask them if they're interested in personality (or psychology). But the type frequency pattern at both forums (involving relatively large samples) is almost perfectly in line with a type-related explanation that says that (1) an N preference has a very large impact on the likelihood that someone will participate in personality-related internet forums, and (2) introversion also has a substantial impact (but not as large as an N preference).

And as far as that validity support is concerned, the distribution curve of mild and strong preferences is irrelevant.

 

[INTP]

Mbti and big5 doesent measure the same exact thing. There is some correlation between them, but that doesent mean they are the same thing. Even i/e are defined very differently between the two systems..

 

[Jaguar]

Abstract
Journal of Personality Assessment
1993, Vol. 60, No. 2, Pages 290-301

Bipolarity in Jungian Type Theory and the Myers--Briggs Type Indicator
Steven A. Girelli, *Jayne E. Stake*



The standard form of the Myers-Briggs Type Indicator (MBTI; Myers & McCaultey, 1985) was constructed to measure introversion/extroversion, sensing/ intuiting, and thinking/feeling as single, bipolar dimensions. We tested this assumption of bipolarity with a Likert form of the MBTI that allowed for the independent assessment of each attitude and function. A total of 106 female and 59 male undergraduate and graduate students completed the standard and Likert MBTI forms approximately 3 weeks apart. Evidence for the bipolarity of the introversion/extroversion dimension was weak, and findings did not support the bipolarity of the sensing/intuiting or thinking/feeling dimensions. Results provide evidence that high negative correlations within MBTI dimensions are an artifact of its forced-choice format.


Is the Myers Briggs system reliable?

This is an extended quotation from the Gale Encyclopedia of Psychology,

"With any psychological test, its use is dependent on its reliability and validity. A reliable test is one that produces consistent results over time. For example, IQ tests have high reliability, inasmuch as your IQ as measured today will not be appreciably different a year from now. The MBTI's reliability is only fair. One study showed that fewer than half of the respondents retained their initial types over a 5-week period. Consequently, we should be careful about making career decisions based on a classification system that is unstable. People change over time as a result of experience. The MBTI may capture a person's current state, but that state should probably not be treated as a fixed typology. Does the MBTI assist in career counseling? Is the test diagnostic of successful performance in particular occupations? These questions pertain to validity-the ability of the test to predict future performance. There have been no long-term studies showing that successful or unsuccessful careers can be predicted from MBTI profiles. Nor is there any evidence that on-the-job performance is related to MBTI scores. Thus, there is a discrepancy between the MBTI's popularity and its proven scientific worth. From the point of view of the test-taker, the MBTI provides positive feedback in the form of unique attributes that are both vague and complimentary, and thus could appeal to large numbers of people. It is possible that the MBTI could be useful as a vehicle for guiding discussions about work-related problems, but its utility for career counseling has not been established."

Personality testing and, MBTI in particular, is here found to be of "only fair" reliability and its use, even in career counseling, doubtful.

 

[reckful]

Mbti and big5 doesent measure the same exact thing. There is some correlation between them, but that doesent mean they are the same thing. Even i/e are defined very differently between the two systems..

Ya, I'm sure the real, underlying introverty thing that the MBTI E/I dimension is tapping into and the real, underlying introverty thing that the Big Five E/I dimension is tapping into are two different things.

Thank goodness we've got both typologies, eh? We wouldn't want to miss either of those introversions!

And the point is...

The fact that the MBTI and Big Five may differ significantly (and they do!) in the way they theoretically characterize what the dimensions are all about doesn't mean that, if you switch your focus from the theoretical level to the underlying-biology level, the real, underlying (and at least somewhat hardwired) personality dimensions the typologies are tapping into aren't the same.

McCrae and Costa (the leading Big Five psychologists) certainly think that's the case, and so do most respectable sources, as I understand it.

 

[uumlau]

Wrong. Internally consistent systems in psychology can be assumed to be automatically valid. I didn't miss your point; I disagree. If two separate internally consistent systems agree, then they are more valid. That's how it works.

This is the origin of confirmation bias, which is especially more likely in the soft sciences, no matter how acceptable it is. The study of cross-cultural psychology in recent years has revealed that a lot of the results we see in Western culture are unique to Western culture, and are only tangentially related to psychology understanding of the human mind.

At issue is the intrinsic difference between between reliability and validity. What your OP demonstrates is reliability, but as Hard points out, it fails to demonstrate validity. A handy analogy is the old joke about the drunk looking for his keys, where the drunk is looking for his keys under the streetlight, even though he knows he dropped his keys over there in that dark corner. Looking in the dark corner would be valid, but unreliable, as it is difficult to get results from the corner. Looking under the streetlight is reliable, but invalid, because we know that the keys weren't dropped near there. We could feel around in the dark corner, find a jingly metal object that feels like keys, but (in this analogy), there would be nothing to publish a paper about, because we have no light here to prove that we actually found the keys. We would "know" that they were the drunk's keys, because we know what "keys" feel like and it isn't likely that there are someone else's keys here, but "it feels like keys" isn't good enough for those who need a reliable light on the subject.

This is not to say that MBTI or Big Five are invalid, only that their similarity does not lead to the conclusion that they are valid.

This ends up playing out in various debates in typology, for example, in comparing cognitive functions to MBTI and Big Five. Those who believe function theory to be wrong will spend thousands of words pointing out how demonstrably reliable MBTI and Big Five are, while function theory has no such reliability. Those who work with function theory, on the other hand, see the functions play out in (necessarily anecdotal) case after case, with a (personal) degree of validity much greater than MBTI, and don't seem to be easily persuaded on the basis of reliability of MBTI and Big Five that function theory therefore has no basis in fact.

We need both reliability AND validity, in order to truly know what is true or not. In the soft sciences, we often tend to have either one or the other, but rarely both. (If we could get both, then they'd not really be soft sciences any more.)