When stratified by true tertiles , 30-day and 1-year rates of definite/probable ST were significantly greater in the highest tertile ( SS > 12 ; 2.0 % and 2.8 % ) compared with the intermediate ( SS = 7-12 ; 0.7 % and 1.1 % ) and lowest tertiles ( SS < 7 ; 0.6 % and 0.7 % ) , P = 0.007 and P = 0.0009 , respectively .