Back to table of contents Previous article Next article Communications and UpdatesFull AccessDeficiency of the Odds Ratio for Common OutcomesJay S. Kaufman, Ph.D., and Sam Harper, Ph.D.Jay S. KaufmanSearch for more papers by this author, Ph.D., and Sam HarperMontreal, QuebecSearch for more papers by this author, Ph.D.Published Online:1 Oct 2012https://doi.org/10.1176/appi.ajp.2012.12060800AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To the Editor: The article by Chen et al. (1) in the July issue provides a fascinating account of the interaction by genotype in the context of a smoking cessation trial. Participating smokers were randomly assigned either to placebo (N=132) or to various combinations of active treatments (N=941). The authors then reported the proportion with confirmed 7-day abstinence after 8 weeks, stratified by three common haplotypes (defined by two single-nucleotide polymorphisms on chromosome 15 that have established associations with nicotine and cocaine dependence). Despite clear evidence of statistical interaction between haplotype group and successful smoking cessation, the authors’ stated conclusion that “[s]mokers with the high-risk haplotype were three times as likely to respond to pharmacologic cessation treatments as were smokers with the low-risk haplotype” is not correct. As shown in Figure S4 of the online data supplement that accompanies the Chen et al. article, treatment approximately doubled (not tripled) the 8-week abstinence proportion in the high-risk haplotype group, from about 24% to about 50%. In contrast, there was no treatment effect in the low-risk haplotype group.The explanation for this large discrepancy is that the authors made the common error of interpreting odds ratios from logistic regression models as relative risks. This interpretation is not valid for outcomes that are not rare. It has been repeatedly noted in the biomedical literature that this is a serious deficiency of the odds ratio (2, 3), and many authors have therefore urged that for cohort analyses such as those used in the Chen et al. study, the odds ratio is not a parameter of interest and should be avoided (4). It is simple in these settings to estimate risk ratios or differences (5), and this also facilitates useful calculations such as the number needed to treat (i.e., the inverse risk difference) (6). For example, manipulation of these absolute risks shows that the number needed to treat in order to prevent one relapse among the high-risk haplotype subpopulation is approximately four. This is an impressive finding that is completely obscured in the published analysis.Montreal, QuebecThe authors report no financial relationships with commercial interests.References1 Chen LS, Baker TB, Piper ME, Breslau N, Cannon DS, Doheny KF, Gogarten SM, Johnson EO, Saccone NL, Wang JC, Weiss RB, Goate AM, Bierut LJ: Interplay of genetic risk factors (CHRNA5-CHRNA3-CHRNB4) and cessation treatments in smoking cessation success. Am J Psychiatry 2012; 169:735–742Link, Google Scholar2 Altman DG, Deeks JJ, Sackett DL: Odds ratios should be avoided when events are common. BMJ 1998; 317:1318Crossref, Medline, Google Scholar3 Schwartz LM, Woloshin S, Welch HG: Misunderstandings about the effects of race and sex on physicians’ referrals for cardiac catheterization. N Engl J Med 1999; 341:279–283; Discussion 286–287Crossref, Medline, Google Scholar4 Knol MJ, Duijnhoven RG, Grobbee DE, Moons KG, Groenwold RH: Potential misinterpretation of treatment effects due to use of odds ratios and logistic regression in randomized controlled trials. PLoS ONE 2011; 6:e21248Crossref, Medline, Google Scholar5 Austin PC: Absolute risk reductions, relative risks, relative risk reductions, and numbers needed to treat can be obtained from a logistic regression model. J Clin Epidemiol 2010; 63:2–6Crossref, Medline, Google Scholar6 Bender R, Kuss O, Hildebrandt M, Gehrmann U: Estimating adjusted NNT measures in logistic regression analysis. Stat Med 2007; 26:5586–5595Crossref, Medline, Google Scholar FiguresReferencesCited byDetailsCited ByNicotine & Tobacco Research, Vol. 20, No. 4Association Between Farm Machinery Operation and Low Back Disorder in FarmersJournal of Occupational & Environmental Medicine, Vol. 58, No. 6 Volume 169Issue 10 October 2012Pages 1118-1118 Metrics PDF download History Accepted 1 August 2012 Published online 1 October 2012 Published in print 1 October 2012