Why is this sentence correct? Why is the subject "students" or "they" omitted in "as did just a decade ago"? Can someone shed light on this peculiar construction and point to an online resource that gives a clear explanation? And what is the name for this kind of sentence construction?
"Only half as many students study computer science as did just a decade ago."
Pope of the Dictionary.com Forum
Ellipsis (linguistics) - Wikipedia, the free encyclopedia
It states that:
" At other times, however, ellipsis seems to be obligatory, for instance with cases of comparative deletion, e.g. *More girls were there today than girls were there yesterday. The second occurrence of girls must be omitted in this sentence (More girls were there today than were there yesterday)."
That puts my doubts to rest.
Thanks for your detailed reply. Since you mentioned ellipsis in your answer, I looked it up online and was able to find further explanation of ellipsis in comparative deletion in Wikipedia.