JRMS J Res Med Sci Journal of Research in Medical Sciences Journal of Research in Medical Sciences 1735-1995 1735-7136 Medknow Publications Pvt Ltd India JRMS-18-1118 24523809 Letter to Editor Obesity predictors in people with chronic spinal cord injury: Common mistake Sabour Siamak Department of Clinical Epidemiology, Safety Promotion and Injury Prevention Research Centre, Shahid Beheshti University of Medical Sciences, Tehran, Iran Address for correspondence:Siamak Sabour, Department of Clinical Epidemiology, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran s.sabour@sbmu.ac.ir December 2013 18 12 1118 1118 Copyright: © Journal of Research in Medical Sciences 2013

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<p>Sir,</p> <p>I was interested to read the paper by Sabour. H and colleagues published in J Res Med Sci in March 2011. <sup> <xref ref-type="bibr" rid="ref1">1</xref> </sup>The purpose of the authors was to assess obesity predictors of people with spinal cord injury (SCI) using a cross-sectional study.Why did the authors use a cross-sectional design! For prediction studies, we need two different sets of cohort data or at least one cohort dataset splitting that to develop our prediction model and then to validate it. Therefore, by using a cross-sectional design, we cannot say anything about prediction. <sup> <xref ref-type="bibr" rid="ref2">2</xref> </sup>, <sup> <xref ref-type="bibr" rid="ref3">3</xref> </sup>, <sup> <xref ref-type="bibr" rid="ref4">4</xref> </sup></p> <p>As the authors pointed out, waist circumference (WC) is classified based on Standard Classification (men >102 cm, women >85 cm). Standard classification for WC is not applicable for the Iranian population as there is no difference between men and women regarding mean WC. <sup> <xref ref-type="bibr" rid="ref5">5</xref> </sup></p> <p>Therefore, applying such a classification will actually lead to overestimation of the obesity in women as well as underestimation of the outcome in men.</p> <p>Because self-reported height and weight were used in this study, validity (accuracy) and reliability (precision) of the data cannot be guaranteed. Moreover, these variables have been used to calculate another variable such as body mass index (BMI)! Thus, any interpretation based on these variables cannot be clinically correct. Most of the times, misleading results can easily affect the main results and conclusions of such researches.</p> <p>Moreover, for prediction purposes, using the Pearson Correlation Test is one of the common mistakes in reliability analysis as well as prediction researches. <sup> <xref ref-type="bibr" rid="ref2">2</xref> </sup>, <sup> <xref ref-type="bibr" rid="ref3">3</xref> </sup>, <sup> <xref ref-type="bibr" rid="ref4">4</xref> </sup></p> </sec> </body> <back> <ref-list> <ref id="ref1"> <label>1</label> <nlm-citation citation-type="journal"> <person-group person-group-type="author"> <name> <surname>Sabour</surname> <given-names>H</given-names> </name> <name> <surname>Javidan</surname> <given-names>AN</given-names> </name> <name> <surname>Vafa</surname> <given-names>MR</given-names> </name> <name> <surname>Shidfar</surname> <given-names>F</given-names> </name> <name> <surname>Nazari</surname> <given-names>M</given-names> </name> <name> <surname>Saberi</surname> <given-names>H</given-names> </name> <etal /> </person-group> <article-title>Obesity predictors in people with chronic spinal cord injury: An analysis by injury related variables</article-title> <source>J Res Med Sci</source> <year>2011</year> <volume>16</volume> <fpage>335</fpage> <lpage>9</lpage> </nlm-citation> </ref> <ref id="ref2"> <label>2</label> <nlm-citation citation-type="journal"> <person-group person-group-type="author"> <name> <surname>Jeckel</surname> <given-names>JF</given-names> </name> <name> <surname>Katz</surname> <given-names>DL</given-names> </name> <name> <surname>Elmore</surname> <given-names>JG</given-names> </name> <name> <surname>Wild</surname> <given-names>DM</given-names> </name> </person-group> <article-title>Epidemiology.Biostatistics and Preventive Medicine</article-title> <source>rd ed</source> <year>3 rd</year> <volume></volume> <fpage></fpage> <comment>Epidemiology Biostatistics and Preventive Medicine 3 rd ed Philadelphia, PA, United States: Saunders, Elsevier; 2007</comment> </nlm-citation> </ref> <ref id="ref3"> <label>3</label> <nlm-citation citation-type="journal"> <person-group person-group-type="author"> <name> <surname>Rothman</surname> <given-names>KJ</given-names> </name> <name> <surname>Greenland</surname> <given-names>S</given-names> </name> <name> <surname>Lash</surname> <given-names>TL</given-names> </name> </person-group> <article-title>Modern Epidemiology.3 rd ed</article-title> <source>Baltimore, United States: Lippincott Williams & Wilkins;</source> <year>8</year> <volume></volume> <fpage></fpage> <comment>Modern Epidemiology 3 rd ed Baltimore, United States: Lippincott Williams & Wilkins; 2008</comment> </nlm-citation> </ref> <ref id="ref4"> <label>4</label> <nlm-citation citation-type="journal"> <person-group person-group-type="author"> <name> <surname>Szklo</surname> <given-names>M</given-names> </name> <name> <surname>Nieto</surname> <given-names>FJ</given-names> </name> </person-group> <article-title>Epidemiology Beyond the Basics.2 nd ed</article-title> <source>Manhattan, New York, United state: Jones and Bartlett Publisher;</source> <year>7</year> <volume></volume> <fpage></fpage> <comment>Epidemiology Beyond the Basics 2 nd ed Manhattan, New York, United state: Jones and Bartlett Publisher; 2007</comment> </nlm-citation> </ref> <ref id="ref5"> <label>5</label> <nlm-citation citation-type="journal"> <person-group person-group-type="author"> <name> <surname>Hadaegh</surname> <given-names>F</given-names> </name> <name> <surname>Zabetian</surname> <given-names>A</given-names> </name> <name> <surname>Sarbakhsh</surname> <given-names>P</given-names> </name> <name> <surname>Khalili</surname> <given-names>D</given-names> </name> <name> <surname>James</surname> <given-names>WP</given-names> </name> <name> <surname>Azizi</surname> <given-names>F</given-names> </name> </person-group> <article-title>Appropriate cutoff values of anthropometric variables to predict cardiovascular outcomes: 7.6 years follow-up in an Iranian population</article-title> <source>Int J Obes (Lond)</source> <year>2009</year> <volume>33</volume> <fpage>1437</fpage> <lpage>45</lpage> </nlm-citation> </ref> <ref id="ref6"> <label>6</label> <nlm-citation citation-type="journal"> <person-group person-group-type="author"></person-group> <article-title></article-title> <source></source> <year></year> <volume></volume> <fpage></fpage> </nlm-citation> </ref> </ref-list> </back> </article>