An optimal cutoff value for the SAM-RDI at 20 events/h was obtained by a receiver operator characteristic curve analysis , which yielded a sensitivity of 88.9 % ( 95 % confidence interval [ CI ] 65.3 % -98.6 % ) , a positive predictive value of 88.9 % ( 95 % CI 65.3 % -98.6 % ) , and a specificity of 84.6 % ( 95 % CI 54.6 % -98.1 % ) ( n = 31 ) .