Maarit Huovinen (toim.) & Timo Erkinjuntti & Kari Alhainen & Juha Rinne is currently considered a "single author." If one or more works are by a distinct, homonymous authors, go ahead and split the author.
Maarit Huovinen (toim.) & Timo Erkinjuntti & Kari Alhainen & Juha Rinne is composed of 1 name.