One of the hidden factors in tuition increases at Michigan universities is the expanding “spider web” of administrators who work outside the classroom, according to the Mackinac Center in Midland.

Relying on numbers compiled by the House Fiscal Agency, the Mackinac Center reports that the state’s public universities boosted spending on “academic support services” by 18.7 percent over the past four years. In that same time frame, tuition and fees rose 16 percent.

The fiscal agency defines academic support services as activities “related to instruction, research, and public service,” but not manned by instructors or researchers. In addition to administrators and some college deans, personnel in this category include advisers and people who work at university libraries, museums, and galleries.

Spending on support services rose from $661 million in 2010-11 to $784 million in 2014-15.

The biggest increases were put into place at University of Michigan-Flint, Central Michigan University and Michigan State University.