I automatically use the preposition on after the words focus or emphasis. However, I've recently come across several instances of them being followed by in, such as in the following examples:
She graduated with a degree in studio art, with a focus in printmaking.
He graduated with a degree in creative writing, with emphasis in fiction.
A quick Google search shows that this is common. I'm not entirely convinced however, and I can't seem to find anything to support the use of in in dictionaries or style guides. Any help?