HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Erturk, S. M. Articles by Megibow, A. J. Search for Related Content PubMed PubMed Citation Articles by Erturk, S. M. Articles by Megibow, A. J.

Evaluation of Bowel Distention with a Neutral Contrast Agent: Some Statistical Concerns

Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, One Brigham Circle, 1620 Tremont Street, 3rd Floor Radiology Suite, Boston, MA 02120
e-mail: serturk{at}partners.org

Editor:

I read with great interest the article by Dr Megibow and colleagues (1) in the January 2006 issue of Radiology. I have some concerns about the Materials and Methods and Results sections of this article.

In the Materials and Methods section, under the subtitle "Statistical Analysis," the authors state that the two groups included in their study were compared with respect to the mean values for each segment of the gastrointestinal tract (stomach, duodenum, jejunum, and ileum) by using the Mann-Whitney test, and they add that the combined mean scores were compared at a 95% confidence level by using the Wilcoxon signed rank test. As it is known, whereas a Mann-Whitney U test is used when ordinal data are obtained in the independent groups situation, a Wilcoxon signed rank test is used when ordinal data are obtained in the paired samples situation (2). In this case, the use of a Mann-Whitney U test seems appropriate since the two groups were composed of different patients. Nevertheless, it is not clear which test was really employed by the authors.

In the Results section, under the subtitle "Qualitative Analysis," the authors report that the mean value for distention in the ileum was significantly higher in group 1 than group 2. However, they give a P value of .140 that by definition does not indicate significance at the 5% -error level. This point needs to be clarified.

Finally, since the qualitative image analysis included two independent readers and their combined mean scores were used for statistical comparisons, it might have been meaningful to evaluate the interobserver agreement with statistics.

	References

TOP References

 

1. Megibow AJ, Babb JS, Hecht EM, et al. Evaluation of bowel distention and bowel wall appearance by using neutral oral contrast agent for multi-detector row CT. Radiology 2006;238:87–95.
2. Applegate KE, Tello R, Ying J. Hypothesis testing III: counts and medians. Radiology 2003;228:603–608.[Abstract/Free Full Text]

Response

Department of Radiology, NYU Medical Center, 550 First Avenue, New York, NY 10016
e-mail: alec.megibow{at}nyumc.org

The author has made three observations.

1. Dr Erturk is correct in highlighting the ambiguity of which statistical test was used in analyzing the data. In fact, we used a Wilcoxon "rank sum" test (not a "signed rank" test). The Mann-Whitney U test is equivalent to the rank sum test, so the results remain valid. We probably should have used a single term (ie, either Wilcoxon rank sum or Mann-Whitney U test throughout). This would have avoided the confusion. Despite the technical terminology, the results of the study are not affected.

2. A P value of .14 is published for differences of ileal distention, and the author of the letter is correct in stating that this does not represent a statistically significant difference. The actual value should have been reported as P = .014 (the true calculated result).

3. We could compute a statistic. However, we believe this result is not germane to the message of the article.

This Article Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Erturk, S. M. Articles by Megibow, A. J. Search for Related Content PubMed PubMed Citation Articles by Erturk, S. M. Articles by Megibow, A. J.