Table 3

Spearman correlation coefficient Logit (sensitivity) vs Logit (1- specificity)

Test

Rifampicin

Isoniazid

Spearman correlation coefficient

p-value

Spearman correlation coefficient

p-value

Nitrate Reductase Assay

0.400

0.600

1.000

0.000

MODS

0.086

0.872

0.143

0.787

Genotype^® MTBDR

0.500

0.667

1.000

0.000

Genotype^® MTBDRplus

-0.200

0.747

-0.100

0.873

MODS = Microscopic Observation Drug Susceptibility. Note: A strong positive Spearman correlation coefficient between the logit of sensitivity and logit of 1-specificity suggests threshold/cutoff effect [27]. Since pooling sensitivity and specificity is more reliable in the absence of a threshold effect the NRA and the Genotype^® MTBDR assays should be primarily judged based on their areas under sROC, while the other tests can be reliably judged based on their pooled values.

Bwanga et al. BMC Infectious Diseases 2009 9:67   doi:10.1186/1471-2334-9-67