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Visual inspection with acetic acid as a cervical cancer test: accuracy validated using latent class analysis

Lynne Gaffikin*, John A McGrath, Marc Arbyn and Paul D Blumenthal

BMC Medical Research Methodology 2007, 7:36  doi:10.1186/1471-2288-7-36

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John McGrath   (2012-08-02 14:47)  Johns Hopkins University

This commentary serves to point out that in the results section (p.7) of the manuscript, we (the authors) incorrectly described the calculation of specificity of VIA for the 3-class model. The corrected text (below) describes a specificity of 0.65 versus 0.57. The calculation correction is also appended.

"Specificity was 0.645. In that model, class 1 (p = 0.682) and class 2 (p = 0.200) combine to form non-disease. Specificity was calculated as 0.323 (probability of VIA inflammation given class 2) plus 0.117 (probability of VIA normal given class 2) multiplied by the probability of class 2 (0.200), plus the analogous values for Class 1, i.e., 0.429 (probability of VIA inflammation given class 1) plus 0.276 (probability of VIA normal given class 1) multiplied by the probability of class 1 (0.682), the entire sum being divided by the probability of non-disease (0.682 + 0.200)."

In Table 4, the specificity values for the 3-class LCA solution reference standard (#4) are likewise incorrect. These values were given as 0.568, 0.820, 0.568, 0.758, and 0.860 for, respectively, VIA Abnormal, CA; Pap LGSIL+; HPV >= 1.0 RLU; Colposcopy/Biopsy LGSIL+; and Colposcopy/Biopsy HGSIL+. The correct values are all higher and should be listed as 0.645, 0.930, 0.644, 0.860, and 0.975.

In keeping with the above, the following text (pages 6-7) should be corrected as follows (0.645 instead of 0.568):

"In this study, despite apparent imperfections in the reference standard, the conventionally-derived VIA results fell within the range of published data and were relatively consistent between with the 3-class LCA model (0.775 versus 0.744, respectively, for sensitivity and 0.639 and 0.645, respectively for specificity)."

These corrections do not substantively alter the results (as noted above, the corrected LCA-derived specificity value is now almost the same as the conventionally derived value, similar to what was observed for VIA for sensitivity) and the corrections do not affect our conclusions.

Competing interests



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