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Table 6 Definitions and formulas used for yield calculations

From: High yield of culture-based diagnosis in a TB-endemic setting

  Description Formula
Ad Number of SE who had specimens examined Px + NP + NN + N9
  Observed # of P SE after 1 specimen Px
Od Observed # of P SE after 2 specimens Px + NP
Sd1 Fraction of SE found positive on the 1st specimen Px/(Px + NP + NN + N9)
Sd2 Fraction of SE found to be negative on the 1st specimen but positive on the 2nd NP/(NP + NN + N9)
Md # of P SE missed by failing to do a 2nd specimen Sd2 * N9
  Expected # of P SE after 1 specimen: same as Observed # of P SE after 1 specimen  
Ed Expected # of P SE after 2 specimens (if all suspects had 2 specimens done) Od + Md
  Expected proportion of P SE after 1 specimen: same as Sd1  
Rd Expected proportion of P SE after 2 specimens Ed/Ad
Fd1 Fraction for the potential IY from the 1st specimen Px / Ed
Fd2 Fraction for the potential IY from the 2nd specimen (Md + NPx) / Ed
OFP1 Overall fraction of P on 1st specimen Rd * Fd1
OFP2 Overall fraction of P on 2nd specimen Rd * Fd2
NND1 NND on 1st specimen: number of specimens needed to be examined to find one additional case 1/OFP1
NND2 NND on 2nd specimen 1/OFP2
  1. Appendix Legend. # = Number, P = positive, SE = Suspect Episodes, NND = number needed to diagnose.