Research to support ID team head count

Summary

Not Learn System related

Content

I figured this might be a good place to ask... does anyone have any research or case studies they've ran across that help support head count? X number of IDs to X number of learners/org size? I know alot of us work on smaller teams. We have already done an internal study on how we use hours, prioritize projects, etc. I'm looking for reputable research on the ideal size of the team based on diversity of workplace knowledge, speed to field, and size of the learners material is being created for.

Basically, what business case did you use to get to the right number of people on your team to support the work you do?