In a narrow study of health care costs associated with a private exchange, employers who offered their workforces health insurance through Aon Hewitt's private exchange said they incurred an average health cost increase of 5.3 percent in 2014. That figure is nearly 2 percent lower than industry averages for large corporations. 

Aon Hewitt said it reviewed the performances of 18 employers who shifted workers to its private exchange. The 5.3 percent cost increase in 2014 compares favorably to estimates released by the National Business Group on Health, which said large companies were reporting 2014 increases in the neighborhood of 7 percent.

Aon Hewitt's survey is the second to be released this month by a large health care consulting firm that offers coverage via a private exchange. Towers Watson pushed out a study last week indicating growing interest in such an insurance coverage model.