I have just read an article about how firstborns are more "go-getters" and last borns are more likely to get in trouble and act out. I have 2 questions:

1) The author quoted a professor at Harvard who asked the class to raise their hands if they were firstborns, of which about 2/3 raised their hand. My first question is, isn't this kind of poll illogical to determine the answer to the issue? Statistically speaking, there is a 100% chance that the parents of each person in the room had at least one child. The percentage of multiple births, however decrease from there. If a child is an only child, they are by default firstborns (disregarding miscarriages, stillbirths, and the like), and if a child is not a firstborn, they HAVE to have at least one other sibling. So if you are a first born, you are one of one, and if you are not a first born, you are one of 2 or 3 or 4, etc, AND you were not the first of those. It's like adding on another stipulation to those who had more than one sibling.
For instance, the prof. would have gotten the same result if he said' "Everyone raise your hand. If you don't have any siblings, keep them up. If you have 1 or more siblings, put your hand down, unless they were all born after you."

What I'm trying to say (sorry it's so lengthy) is that there is a higher percentage of people who were born first if they have no other siblings than of people who were born first with multiple siblings. It's like having a 1/1 chance to be a firstborn vs. a 1/5 chance if you have four siblings. Anyone have any comments on that, or would like to correct my math (statistics isn't my strong suit)?

2) What is the effect when a child has been a firstborn for the first, say, 15 years of their life (or longer), before a sibling came along? What about step siblings? Half sibling that don't live with you? I have 9 siblings, and technically, I would be 7th, but I didn't grow up with all of them, and some of them I was only with for the first years, middle years, or last years, others I have lived with throughout. Is there a way of putting a general label on what kind of person I'd be, based on birth order, in that kind of situation? Forgive me, but I think this is a topic with very limited application due to modern family dynamics. Any comments?

I think they do this more to determine personality than the statistics
It just seems like something to note that the characteristics are very similar often.
2.) Their personality would be more like the only child because they had the 15 yrs growing up without siblings.

It is just a very basic generalized outline of sibling order, there are many other factors to consider.
There definitely is something to it but does need to have other considerations.

Great question! I don't have much to add, but I have the book, Birth Order ( I believe) on my shelf, for ten years or more, but haven't read it yet. I have observed that all children are selfish, naturally enough. And that older kids are resentfully selfish of the younger sibling(s), and younger siblings are happily selfish of all the attention they receive.

The prof. should have asked how many had siblings, and then, of those how many were first born. My sister (just two children) was the first born and she is still a go-getter. But she was two years older and I benefitted from her guidance in school. She had recently experienced what I was going through at present, and I had instant guidance available. So the impact of that close influence may have offset some of the non-gogetter traits. If there is a big age difference, this association is lost, I think.