Health insurance, business insurance, vacation time, holiday time, sick time, equipment, etc. All of these things go into the calculations for your rates.

Contractors are subject to the health care plans of the company they work for (or whatever they buy on the individual market, if they are self-employed). Part-time employees (less than 30 hours per week, IIRC, although that's probably state-by-state) also receive different treatment. Some companies have started to manage hours to have more part-time workers instead of fewer full-time workers as a means to game the heath care laws: http://www.washingtonpost.com/blogs/wonkblog/wp/2013/05/06/w...