An optimal cutoff value for the SAM-RDI at @ events/h was obtained by a receiver operator characteristic curve analysis , which yielded a sensitivity of @ % ( @ % confidence interval -LSB- CI -RSB- @ % -@ % ) , a positive predictive value of @ % ( @ % CI @ % -@ % ) , and a specificity of @ % ( @ % CI @ % -@ % ) ( n = @ ) .