Wow, I am flattered my explanation has raised such interests. I'll try to answer as best I can to each question. So you guys don't think we Chinese are that wierd anymore asking about the birth order right?
I have to first verify that there is no scientific study or research to back it up, and we usually use it as a evaluation tool on the person in terms of friendship or romantic relationship and the prospect of it. It's no more accurate than asking about favorite past-time activity. Anyway, I'll start with the easier one to answer.
Formatto: Please tell me the psychology associated with 'an only child'.
This is kind of a wild card. It could go one way or the other on the spectrum (am i using this word right?) for apart from the influence of the parents' rearing style, the only child is raised in the most "unconditioned" enviorment, free from the influence of siblings. So one could be a spoiled, self-serving brat while the other too eager to please to gain friendship because he/she's been lonely growing up. Or one could grow up to be somewhat of a delinquent in social skills while other only-child could come across obnocious and loud or a social butterfly, so it heavily depends on the child natural deposition. I hope I'm making sense.
But what if a family has five or six or more children? Do all except the first and last count as "middle children"?
Kind of. We just kind of adjust the indicator on the scale (I'm not sure what I'm talking about in terms of vocabulary.

I know, but I'm trying my best people!). Just bear with me and you'll understand. Let's picture a lineage line with first-born on the far left representing the extreme domineering/controling traite and the youngest on the far left indicating a care-free, optimistic, ect. personality. So it's just a matter of placing or moving the ^ (a mark usually seen on a scale) on the scale according to the number of children in the person's family and his/her birth order. I have to again verify this is no hard measurement on people's personality for there are other factors such as genders, environments and the built-in personality that came with us at birth that cause variants.
Ouisch: And my blood type is A-positive; guess that means I got an A+ on my blood test, eh? ;-)
Angelika: I don't know - in none of my dealings with doctors and hospitals have they ever considered it necessary to find out or to tell me:shock:
David: All things considered, I would prefer being asked about my position in brith order than my starsign
Yes! it is kind of like asking about your starsign (horoscope?) only in a more graphic and obnoxious way. "What's your bloodtype?" what's up with that?
I remember the first time I asked this question to an American, he acted so incredulous that I wondered if I had asked to borrow money from him. I wouldn't be surprised if he suspected that I needed a blood transfusion. Anyway, as with birth order, this has no hard scientific evidence and I don't know how it started. We just knew what our blood types are and what each bloodtype reprents, and here they are:
Type A: sincere, gentle, considerate, loyal, worry-prone, self-righteous, secretly judgemental.........
Type B: calm, peaceful, easy-going, family-oriented, unmotivated, undriven...
Type AB: fun-loving, loud, trusting, care-free, easily happy, obnoxious, disorganized, irrepsonsible..........
Type O: domineering, intimidating, controling, fast-pacing, driven, inpatient, insensitive............
There're a whole long list to each type, I just listed the core traits. Like I said I don't know how it started. I used to think the whole world used this method and the method is widespread but little did I know.:-(
So anyway, like Light said, there isn't a question word in English to get the position in birth order right? I still think there could have been though, if the native speakers ancestors had been introduced to such theory, they would have come up with
the question word, right?
NT