"Core beliefs," eh?
There's now over 50 years of data — from hundreds of studies in peer-reviewed journals and so on — that strongly suggests that there are a handful of human personality dimensions that (1) are multifaceted (i.e., that involve multiple characteristics that tend to co-vary in a statistically meaningful way), (2) tend to be relatively stable through life, and (3) are substantially genetic. The "Big Five" is an umbrella term for several somewhat independently-developed typologies with respect to which respectable amounts of data have been gathered and that seem to basically involve the same five underlying dimensions (notwithstanding some theoretical variations from typology to typology and from typologist to typologist), and the four MBTI dichotomies appear to be tapping into four of the Big Five factors — albeit, again, with various theoretical variations both between the MBTI and Big Five and among different MBTI theorists.
In the modern world of personality typology, the relevant scientific standards include judging typologies in terms of two broad criteria known as
reliability and
validity. Reliability basically has to do with internal consistency, while validity relates to the extent to which the theoretical constructs actually relate to reality. Going all the way back to 1985, the second edition of the MBTI Manual devoted two chapters to the issues of reliability and validity, and there's been substantial additional confirmation in the years since.
McCrae and Costa are probably the most prominent Big Five scientists, and they long ago concluded (see
this article) that the four MBTI dichotomies were essentially tapping into four of the Big Five factors, and that there was respectable scientific data in support of the MBTI dichotomies.
Over twenty years ago now, John B. Murray ("Review of Research on the Myers-Briggs Type Indicator," Perceptual & Motor Skills, 70, 1187, 1990) summed up the MBTI's status this way:
Here are three more sources, if you're interested. Each of the last two includes a roundup of multiple studies.
Hierarchical Confirmatory Factor Analysis of the MBTI
MBTI Form M Manual Supplement
MBTI Step II Manual Supplement
Particularly noteworthy (to me, anyway) is the fact that twin studies have established that identical twins
raised in different households are substantially more alike with respect to the Big Five and MBTI dimensions than more genetically dissimilar pairs, which strongly suggests that these typologies are tapping into personality dimensions that are relatively hard-wired — however imperfectly and/or incompletely grasped and defined they may be at this stage.
I should probably also note, though, that the data support for the MBTI relates almost exclusively to the four MBTI
dichotomies — which correlate with four of the Big Five dimensions — rather than the eight "cognitive functions." As I understand it, and as further discussed in
this long INTJforum post, the few attempts to test/validate the functions — and, in particular, the functions model most often discussed on internet forums (where INTJ = Ni-Te-Fi-Se and INTP = Ti-Ne-Si-Fe) — have not led to a respectable body of supporting results.
As for "core beliefs"... I'll confess I'd never even heard of them. So I tried to check out the Wikipedia article, but dang, there isn't one! So then I Googled "core beliefs," and danged if I've been able to find any reference to any psychological theory that goes by that name and has any respectable body of studies behind it.
But OK, I'll admit I didn't spend
that long searching. Hopefully you can steer me to two or three respectable sources that will explain to me what the "core beliefs" system is all about and help convince me and any other deluded forumites that "core beliefs" have left extraversion/introversion and the rest of the Big Five and MBTI dimensions in the dust.
any psychologists on this forum maybe want to chime in?? 
