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McNemar Test Is Preferred for Comparison of Diagnostic Techniques

Chung Shan Medical University Hospital Taichung, Taiwan
Corresponding Author, Taichung Veterans General Hospital Taichung, Taiwan

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We read with interest the well-written article in the January 2008 issue of AJR, "MDCT and Radiography of Wrist Fractures: Radiographic Sensitivity and Fracture Patterns" by Welling et al. [1]. Using MDCT as a reference standard, the authors reported 30% of wrist fractures were not prospectively diagnosed on radiography. The authors noted a significant relationship between radiographic reports and MDCT findings for scaphoid (p = 0.003), pisiform (p = 0.02), trapezium (p = 0.005), distal radius (p < 0.001), ulna (p < 0.05), and proximal metacarpal (p < 0.05) fractures using the chi-square and Fisher's exact tests for comparison.

Comparative radiologic studies commonly produce matched data because all the diagnostic tests under comparison are performed on the same subject [2, 3]. Use of a chi-square or Fisher's exact test in the technique-comparison study of related samples is inappropriate [4]. A more appropriate statistical test for the study of Welling et al. [1] would be a McNemar test or its exact form for related samples [3, 4].

We performed the exact form of the McNemar test on the findings of Welling et al. [1], comparing radiographic reports and CT findings for scaphoid (p = 0.004), lunate (p = 0.625), triquetrum (p = 0.688), pisiform (p = 1.0), trapezium (p = 1.0), trapezoid (p = 0.25), capitate (p = 1.0), hamate (p = 1.0), distal radius (p = 1.0), ulna (p = 0.5), and proximal metacarpal (p = 0.5) fractures. From the data provided by the authors [1], MDCT is superior to radiography in detecting scaphoid fractures but not other wrist fractures.

References

1. Welling RD, Jacobson JA, Jamadar DA, Chong S, Caoili EM, Jebson PJ. MDCT and radiography of wrist fractures: radiographic sensitivity and fracture patterns. AJR 2008;190 : 10–16[Abstract/Free Full Text]
2. Joseph L, Reinhold C. Statistical inference for proportions. AJR 2005; 184:1057 –1064[Free Full Text]
3. Dwyer AJ. Matchmaking and McNemar in the comparison of diagnostic modalities. Radiology 1991;178 : 328–330[Abstract/Free Full Text]
4. Mann FA, Hildebolt CF. Inappropriate use of a chi 2 test in modality comparison study of related samples. (letter) Radiology 1991;178 : 582–583[Medline]

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				E. M. Caoili and J. A. Jacobson Reply Am. J. Roentgenol., October 1, 2008; 191(4): W191 - W191. [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Liao, Y.-Y. Articles by Lin, Y.-M. Search for Related Content PubMed Articles by Liao, Y.-Y. Articles by Lin, Y.-M. Social Bookmarking                      What's this? Hotlight (NEW!) What's Hotlight?