It may be, but you have to check for a ceteris paribus condition of everything else. Thus, I expect that IRL the correlation becomes extremely spurious, to the point of non recognizability.
As I believe I said though, If it's possible to isolate one variable in a large enough study by determining the true/false value in every test case, the other variables will become statistically insignificant.
For example, if I want to figure out if red cubes are heavier on average than blue cubes, I simply split the cubes into two groups and weigh every cube. If I have 10,000 cubes total, the material and size of each cube becomes insignificant on the whole. (Though I suspect I would find red and blue cubes are approximately equal in weight, statistically )
I think there is definitely something to this. My situation is a bit different, as I'm the youngest of two, but my older brother has always been mentally handicapped and so in a sense I've taken on the role of the older sibling --- but it's not the same as being an actual first born child. I'm an INFP but I'm very close (almost right on) the T border.
However, birth order is something I'm extremely interested in, largely because of my own uncommon experience. One thing I've recently noticed (without even having the MBTI in mind) is that every single person I've ever seriously dated (this is 4-5 people depending on what you consider "serious") has been the first born child with younger siblings. It just so happens that intellectual independence is extremely important/necessary to me in a partner, second only to if not tied with compassion. So obviously, all have had this trait. I've noticed a few posts on introversion and birth order, so I'll note that 80% of the time they've been introverted.
this is a nurture thing, not a nature thing. birth order itself would not be the cause of this. my older brother is ehh debating, i would like to say im ok, and my younger sister is good if she knows what she is talking about.
"Honest differences are often a healthy sign of progress. "
"You must not lose faith in humanity. Humanity is an ocean; if a few drops of the ocean are dirty, the ocean does not become dirty."
I saw this in my kids. Son thought his older sister was his mom. Thought she was God, actually.
But recently my son came near death and his sister was crying and saying, "He can't die! He's my twin." I never knew she felt that way.
"No ray of sunshine is ever lost, but the green which it awakes into existence needs time to sprout, and it is not always granted to the sower to see the harvest. All work that is worth anything is done in faith." - Albert Schweitzer
I'm lucky in that I have a very close friend who grew up in a startlingly similar family situation as I did; it's great for comparisons such as these.
He and I are 3 days apart in age, and the eldest of 4 kids. Our sisters are 3 years younger, our brothers are 5 years younger, and our youngest sisters are 7 (him) and 8 (me) years younger.
He: ENFP with ENFP mom and INTJ dad. Me: INTJ with ENFP dad and ISFJ mom.
Basically, we both agree that our younger siblings get away with more than we did at their age, and also that as our parents get more practiced, it shows with their parenting skills. We both feel we had to "work them in" yet didn't reap the benefits because it took a while for our parents to get the hang of things.
From our conversations, I had the harder time of us two considering the fact that I grew up in a household full of very xxFx types (my iNtJ being a small "t" is learned, not natural). Our youngest sisters are both xSFJs, and I don't see any correlation to sibling order regarding intellectual independence, only MBTI.
*You don't have a soul. You are a Soul. You have a body.
*Faith is the art of holding on to things your reason once accepted, despite your changing moods.