require(dplyr)

sum(d$nbi > threshold & d$positive)

sens_spec <- function(pos, neg){
    
    tp <- dim(pos %>% filter( lit))[1]
    fp <- dim(pos %>% filter(!lit))[1]
    
    fn <- dim(neg %>% filter( lit))[1]
    tn <- dim(neg %>% filter(!lit))[1]
    
    return(list(
        sens = tp / (tp + fn),
        spec = tn / (tn + fp),
        prec = tp / (tp + fp),
        neg  = tn + fn,
        pos  = tp + fp,
        fpr  = fp / (fp + tn),
        fnr  = fn / (tp + fn),
        fdr  = fp / (tp + fp),
        tp   = tp,
        fp   = fp,
        tn   = tn,
        fn   = fn,
        n    = tp + fp + tn + fn
    ))
    
}