I came across a weird sentence in a paper. I wonder if its phrasing is correct grammatically since it doesn't make much sense to me.
Since 1991, the number of children with a mother in prison more than doubled, up 131% and children with a father in prison increased by 77%.
I have seen no such usage before where an adjective follows "more than". Is there something I don't know about such structure, or that the author has used a grammatically poor statement?
This usage is correct. Here, more than is used with a verb. Look at the sentence
The number of children doubled.
The verb here is "doubled," meaning "increased to a new amount that is twice the original amount".
We can use "more than doubled" to mean "increased to a new amount that is more than twice the original amount":
The number of children more than doubled.
This is a normal use of more than for "multiplier" verbs like double or triple. To confirm this, you can do a Google search for "more than doubled", which shows the phrase used by Time magazine and official agencies like the CDC.
Using more than with adjectives is also normal (but that is not what is happening in your example):
She is more than angry; she is furious.
They are more than just strong; they are also very fast and smart.
