We thank Drs Lancelot, Piednoir, and Desché for their interest in our work and their comments regarding our recent article.1 However, we disagree strongly with the critique presented in their letter. The necessity to comply with word count limitations when preparing manuscripts for publication means that the description of the statistical methodology is often too brief. We now address the points raised.
Statistical Analysis and Sample SizeThe study design and analysis described in our article 1 are similar to the methodology used in many previous intraindividual comparative studies. [2][3][4][5][6][7][8][9] The primary study end point was the overall diagnostic preference of each of 3 readers for one gadolinium-based contrast agent (GBCA) over the other. Other qualitative end points (determinations of lesion border delineation, definition of disease extent, visualization of lesion internal morphology, and lesion contrast enhancement) are accepted clinically relevant parameters that can directly impact patient management decisions and surgical planning, particularly for patients with glial tumors in whom macroscopically complete surgical removal is associated with improved prognosis and longer patient survival, and those with metastases, for whom determination of the precise number, size, and location of lesions can aid selection of the most appropriate treatment option.3,6-9 Image assessment was performed by comparing images from the 2 MR imaging examinations sideby-side, with the readers blinded to the contrast agent used and all clinical information. Each reader expressed preference for examination 1 or 2 or determined that the 2 examinations were equal. The resulting data for each reader were 1 observation per patient (ie, 1 paired sample datum with an ordinal scale). Nonparametric analysis with a 2-sided Wilcoxon signed rank test is the appropriate statistical analysis method for assessment of overall diagnostic preference. The distribution of the preference between the 2 examinations was also tested by using a 1-sample 2 test for equal proportions. The results obtained were similar to those from the Wilcoxon signed rank test. This analysis was not included in the article due to the word restrictions.The results for Study Arm 1 revealed a highly significant (P Ͻ .0001) preference for gadobenate over gadoterate at an equivalent dose for each reader (Fig 1). Variation of measurements between readers is expected in a fully blinded read setting. Figure 1 shows that all 3 readers were in high agreement and consistent, especially concerning the very few assessments in which gadoterate was preferred over gadobenate (1.6%-3.2% of patients across 3 readers). The major reason for the 50.8% agreement among readers was the differential percentage of preferences for gadobenate across the 3 readers (49.2%, 82.3%, 69.4%). As already discussed in our article, 1 a value of 0.273 was due to the skewed distribution of preferences (very few preferences for gadoterate). Feinstein et al 10 demonstrated clearly that a low can resu...