The new Oxford edition, which will be available in November, was edited by four Shakespeare scholars: Gary Taylor of Florida State University, John Jowett of the University of Birmingham, Terri Bourus of Indiana University and Gabriel Egan of De Montfort University.This research is a great demonstration of the power of computational linguistics. It's similar to some of the past research I've blogged about, such as this study using sentiment analysis of Trump's tweets. In fact, see this recent post on Natural Language Processing for a more in-depth look.
Taylor tells NPR the conclusion that Marlowe should be credited as co-author is partly based on a combination of new and old research. In particular, Taylor cited 2009 research by Hugh Craig and Arthur Kinney that analyzed vocabulary from the Henry VI plays and compared it to plays known to have been written by Marlowe, and a 2015 article by John Nance analyzing the prose of Part 2 of Henry VI.
Taylor himself has published scholarly work on Marlowe and Shakespeare, including work from last year titled Imitation or Collaboration? Marlowe and the Early Shakespeare Canon, on which he collaborated with Nance.
To put it very simply, every writer, no matter how they were taught or who influenced them, has their own unique style. Some of the unique characteristics are very subtle - simple word choice or sentence length. Others are more noticeable. And of course, writers from the same period and genre will be more similar to each other. So based on the fact that both playwrights were active at the same time in the same location, and dealing with similar content, we would expect Shakespeare's writing to be more similar to Marlowe than, say, Isaac Asimov.
But even after taking that into account, there will be some slight differences. So if the writing of Shakespeare is more similar to Marlowe than we would expect based on their similarity in approach and paradigm, we can start to speculate that the two may have been collaborators, rather than simply rivals. This is hinted at in the film Shakespeare in Love, where Shakespeare discusses his writer's block with Marlowe, and gets some advice and direction for the play that would become Romeo and Juliet. This short scene isn't surprising considering that people have been speculating about Marlowe's role in Shakespeare's plays for a very long time. But while a person may read the work of two writers and notice similar patterns, a computer can really dig into the data. Just as statisticians test against a null hypothesis (that a relationship does not exist) and estimate the probability that if there is no relationship we would observe a difference, these analyses can estimate the probability that, if the two authors did not work together, we would see such similarity in vocabulary and style.
Obviously, there could be alternative explanations for the similarities. One strong possibility is offered in the article:
Carol Rutter, a professor of Shakespeare and performance studies at the University of Warwick, told the BBC, "It will still be open for people to make up their own minds. I don't think [Oxford University Press] putting their brand mark on an attribution settles the issue for most people."
Rutter told the BBC, "I believe Shakespeare collaborated with all kinds of people ... but I would be very surprised if Marlowe was one of them."
As for how Marlowe's vocabulary and style could have made it into Shakespeare's work without direct collaboration, Rutter said: "It's much more likely that he started his career working for a company where he was already an actor, and collaborated not with another playwright but with the actors — who will have had Marlowe very much in their heads, on the stage, in their voices. ... They were the ones putting Marlowe's influence into the plays."