The second entity that has been omitted from the analysis is material suppliers, which include manufacturers and retailers that deliver steel, lumber, windows, drywall, etc. (turnkey suppliers that also install the materials are considered subcontractors). While the task expertise and safety expertise of office managers and outside salespersons may be mixed, the expertise of the employees delivering the materials is generally quite low. The factors relating to worker interaction and site presence are low because material suppliers are so infrequently on-site. The factors relating to controlling worker behavior and controlling the site are both low because material suppliers lack both the needed expertise and the authority.