Complex sentence: In 2010 a new supplemented Spetzler-Martin system (SM-supp, Lawton-Young) was devised adding these variables to the SM system, and was determined to have greater greater predictive accuracy that Spencer-Martin grades alone.
Split into simpler sentences: In 2010 a new supplemented Spetzler-Martin system (SM-supp, Lawton-Young) was devised adding these variables to the SM system. It has since been determined to have greater greater predictive accuracy that Spencer-Martin grades alone.