I find it a bit hard to believe marketing of computers alone explains such spectacular drop in one specific area - was physics or chemistry marketed to girls in 80s? Also, how exactly marketing for boys made half of the girls drop the field - as opposed to no marketing? That sounds like too big an effect. Also, one of the ads (other one is unreachable) shows both boys and girls behind the computer and a woman leading the computer class (BTW, famous Apple 1984 ad also featured a woman in a role clearly meant to be associated with the product). How that alone should cause half of the girls to go away? True, nerd usually meant boy. But wasn't it true for physics or chemistry or biology or many other things too? I mean, to identify the key factor you need to do two things a) find that the factor is present when the effect is present (parents buy computers more for boys) and b) find that the effect is not present when the factor is not present (parents do not buy more chemistry sets, physics books, math books, etc. for boys than for girls). I don't see the second part was done. Without it, I think the link can not be established.

Perhaps because it used to be (or be perceived) more like a science back then?