[jsmeaton]

This is one I've been wondering about for awhile:

http://chronicle.nytlabs.com/?keyword=cooperation.co-operati...

I thought the change happened somewhere around the 80-90's. Guess it depends on the country also.

[_delirium]

The Google Books dataset suggests the crossover point was around 1905 in AmE, but not until the late 1970s in BrE (modulo the usual caveats about how their data isn't necessarily a representative sample):

AmE: https://books.google.com/ngrams/graph?content=cooperation%2C...

BrE: https://books.google.com/ngrams/graph?content=cooperation%2C...

[IvyMike]

I think there's a general trend towards dropping the hyphen in common words.

Knuth talks about this in his discussion over "e-mail" v "email": http://www-cs-faculty.stanford.edu/~uno/email.html

[yxhuvud]

It is too bad it doesn't differentiate between cooperation and coöperation.

[_delirium]

Google's version includes coöperation, but it has negligible usage: https://books.google.com/ngrams/graph?content=cooperation%2C...

On the other hand it's possible OCR is missing some of those ¨ and screwing up the data.