Relative impact of the different levels of education on the physical and mental components of SF-12 across the different chronic disorders. Relative impact of the different levels of education on the physical and mental components of SF-12 across the different chronic disorders. University education level was always considered the reference category, that is, the impact of the other education categories on physical and mental components of SF-12 is considered in comparison to university education (SF-12, 12-item Short-Form Health Survey). P Putrik et al. RMD Open 2015;1:e000045 Copyright © BMJ Publishing Group & EULAR. All rights reserved.