[jusben1369]

When I was young I picked up a book at a friend's house on astrology. I am a Taurus. I mistakenly opened it on another sign thinking I was reading the chapter on what made up a Taurus character. I was reading and nodding my head "wow, this is kind of weird. That is me. I do that. Well, I'm not like that but it's not going to be a 100% fit" After several pages I realized my mistake. And then I realized the Forer effect without knowing what it was or that it had a name.

[UrMomReadsHN]

Julia Sweeney on astrology - http://www.youtube.com/watch?v=yVjturKoFsg

(The background is she just found out she was actually born 3 months after her parents told her she was born - they lied to get her to start school a year earlier.)

[hyp0]

Astrology is obviously nonsense, but it seems plausible that the season of birth could have a personality effect: the cold dead of winter, with little fresh food vs spring etc, also from the attitudes of surrounding adults.

Of course, different near the equator, and phase-shifted in the southern hemisphere, and... much less pronounced in modern times, with supermarkets, refrigeration, air-conditioning/heating, imported foods, and wider social presence (newspapers, TV, radio, internet, phone) etc.

[Terr_]

The socially-constructed age-cohort you go into is huge too. Want better grades and performance at sports? Be months older than your classmates.

[allendoerfer]

The reverse is true, too: Want better performance than people of the same age? Have had more training than them.

I suspect this applies especially to language or logic related tasks.

We will likely never find out, variance seems to be extremely high, while the actual differences are very low.

[eru]

There are actual studies. Lots of professional athletes were in the older part of their cohort when they were younger. So the effect Terr_ described seems to outweigh the one you describe.