Most Scrum teams lean toward 7-15 people **, though it's not clear how to scale Scrum among 100s of people, or how the effectiveness of a given team might be compared to another team within the group; meaning beyond just breaking the group into Scrum teams of 7-15 people, it's unclear how efforts between the teams are managed, compared, etc.

Any suggestions related to either of these topics, or additional related topics that might be of more importance to account for in planning a large scale SCRUM grouping?

** In reviewing research related to the suggested size of software development teams, which appears to be the basis for the suggested Scrum team size, I found what appears to be an error in the research which oddly appears to show that bigger teams (15+ ppl), not smaller teams (7 ppl) are better.

UPDATE, "Re: Scrum doesn't scale": Made huge amounts of progress on personally researching the topic, but thought I'd respond to the general belief of some that Scrum doesn't scale by citing a quote from Succeeding with Agile by Mike Cohn :

Scrum Does Scale: You have to admire the intellectual honesty of the earliest agile authors. They were all very careful to say that agile methodolgies like Scrum were for small projects. This conservatism wasn’t because agile or Scrum turned out to be unsuited for large projects but because they hadn’t used these processes on large projects and so were reluctant to advise their readers to do so. But, in the years since the Agile Manifesto and the books that came shortly before and after it, we have learned that the principles and practices of agile development can be scaled up and applied on large projects, albeit it with a considerable amount of overhead. Fortunately, if large organizations use the techniques described regarding the role of the product owner, working with a shared product backlog, being mindful of dependencies, coordinating work among teams, and cultivating communities of practice, they can successfully scale a Scrum project.

SOURCE: (ran across the book thanks to Ladislav Mrnka answer)