Reviewer 1's Review (Elmer V Villanueva)

“Thank you for the opportunity to provide a statistical review of Manuscript 07-PONE-RA-00811 “Interethnic differences in muscle, liver and abdominal fat partitioning on obese adolescents.” The Authors describe the results of a clinical study comparing the differences in fat content and distribution in obese adolescents. My comments relate to the adequacy of the implementation and reporting of statistical procedures.

I can find no major problems from a statistical perspective. The procedures are well-described and adequately referenced.

I have two minor concerns, the adoption of which I leave to in the Authors’ hands. First, the Authors describe the information as being “matched” yet I can find no direct evidence that a matching procedure was used. I can think of two explanations: (1) that matching was actually performed but that the Authors simply forgot to include a description in the manuscript or (2) the Authors interpret “matching” to mean “statistical adjustment”. If the former, the solution is obvious. If the latter, the Authors must remove all claims of “matching” and redirect all statements toward the statistical adjustment procedures actually performed. Either way, the error is easily corrected.

Second, it is usual to test models using established diagnostic methods. This should be performed especially when data-driven variable selection methods are applied (as in the present case in which the Authors used a stepwise analysis). The Authors must describe the results of such diagnostic procedures.

In addition, I have some calls for clarification. All refer to the Figure 1. First, the units for IMCL reported in the text and as stated on the y-axis of the corresponding figure should be brought into congruence. That is, IMCL is reported as a percentage in the text, but in square centimetres in the Figure. Second, the Authors report results for EMCL, but no graph is present. Third, the comparison in visceral fat between Caucasians and African Americans is reported as having p<0.01 in the text but as being p=0.01 in the graph. This needs to be clarified. Where possible, the Authors should consistently report p-values to the same number of decimal places. Finally, the order of the graphs should correspond to the order of the textual description of the results to ease the reading burden on the interested reader.

Apart from these minor issues, I am satisfied with the quality of the work and am happy to support its acceptance for publication. Please pass along my congratulations on a job well done.”

N.B. These are the general comments made by the reviewer when reviewing this paper in light of which the manuscript was revised. Specific points addressed during revision of the paper are not shown.