I need to to reference the report What leads developers towards the choice of a JavaScript framework?.

The authors are

• A. Pano, Free University of Bozen-Bolzano
• D. Graziotin, University of Stuttgart
• P. Abrahamsson, Norwegian University of Science and Technology

I'm not sure how I would reference this using Vancouver notation, since the authors are from different universities?

Is somethings like this correct?

A. Pano, D. Graziotin, P. Abrahamsson, “What leads developers towards the choice of a JavaScript framework?”, Free University of Bozen-Bolzano / University of Stuttgart / Norwegian University of Science and Technology, 2016, 49 pages.

Also, the guide from my university mentions that there should be a "report number" (report code?) in the reference for reports from universities, but I can't find any such number in the referenced report. What is this number, and is it mandatory?