Events per person-time (incidence rate): A misleading statistic?
Corresponding Author
Helena Chmura Kraemer
Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA 943305, U.S.A.
Professor of Biostatistics in Psychiatry (Emerita).
1116 Forest Avenue, Palo Alto, CA 94301, U.S.A.Search for more papers by this authorCorresponding Author
Helena Chmura Kraemer
Department of Psychiatry and Behavioral Sciences, Stanford University, Stanford, CA 943305, U.S.A.
Professor of Biostatistics in Psychiatry (Emerita).
1116 Forest Avenue, Palo Alto, CA 94301, U.S.A.Search for more papers by this authorAbstract
Results in risk studies based on events per person-time (EPT, technically ‘incidence rate’) often prove non-confirmable. The circumstances in which the EPT-ratio is unquestionably both valid and optimal to compare a high- and low-risk group, a constant hazards situation, are discussed. However, the constant hazards situation seldom applies in medical research. When the constant hazards situation does not apply, even under optimal circumstances, with fixed entry time and follow-up time for all those not experiencing the event and absence of censoring, EPT-ratio yields at best ambiguous, at worst misleading, results. More careful design and survival analyses are recommended in place of use of EPTs. Copyright © 2009 John Wiley & Sons, Ltd.
REFERENCES
- 1 Ware JH. The limitations of risk factors as prognostic tools. New England Journal of Medicine 2006; 355(25): 2615–2617.
- 2 von Elm R, Egger M. The scandal of poor epidemiological research. British Medical Journal 2004; 329: 868–869.
- 3 Martyn C. What is the point of epidemiology? Practical Neurology 2004; 4: 192–193.
10.1111/j.1474-7766.2004.01-237.x Google Scholar
- 4 Marshall E. Epidemiologists wary of opening up their data. Science 2000; 290: 28–29.
- 5 Ioannidis JPA. Contradicted and initially stronger effects in highly cited clinical research. Journal of the American Medical Association 2005; 294(2): 218–228.
- 6 Kline RB. Beyond Significance Testing: Reforming Data Analysis Methods in Behavioral Research. American Psychological Association: Washington, DC, 2005.
- 7 Nickerson RS. Null hypothesis significance testing: a review of an old and continuing controversy. Psychological Methods 2000; 5(2): 241–301.
- 8 Wilkinson L. The task force on statistical inference. Statistical Methods in Psychology Journals: Guidelines and Explanations. American Psychologist 1999; 54: 594–604.
- 9 Thompson B. Journal editorial policies regarding statistical significance tests: Heat is to fire as p is to importance. Educational Psychology Review 1999; 11: 157–169.
- 10 Borenstein M. The shift from significance testing to effect size estimation. In Research & Methods, Comprehensive Clinical Psychology, AS Bellak, M Hersen (eds). Elsevier Science Publishing Co.: Burlington, MD, 1998; 319–349.
- 11 Shrout PE. Should significance tests be banned? Introduction to a special section exploring the pros and cons. Psychological Science 1997; 8(1): 1–2.
- 12 Hunter JE. Needed: A ban on the significance test. Psychological Science 1997; 8(1): 3–7.
- 13 Fleiss JL. Significance tests have a role in epidemiologic research: reactions to A.M. Walker. American Journal of Public Health 1986; 76(5): 559–560.
- 14 Altman DG, Schulz KF, Moher D, Egger M, Davidoff F, Elbourne D, Gotzsche PC, Lang T, CONSORT GROUP (Consolidated Standards of Reporting Trials). The revised CONSORT statement for reporting randomized trials: explanation and elaboration. Annals of Internal Medicine 2001; 134(8): 663–694.
- 15 Begg C, Cho M, Eastwood S, Horton R, Moher D, Olkin I, Pitkin R, Rennie D, Schulz KF, Simel D, Stroup DF. Improving the quality of reporting of randomized controlled trials: the CONSORT statement. Journal of the American Medical Association 1999; 276: 637–639.
- 16 Rennie D. How to report randomized controlled trials: The CONSORT Statement. Journal of the American Medical Association 1996; 276(8): 649.
- 17 Last JM. A Dictionary of Epidemiology. Oxford University Press: New York, 1995.
- 18 Newcombe RG. A deficiency of the odds ratio as a measure of effect size. Statistics in Medicine 2006; 25: 4235–4240.
- 19 Kraemer HC. Reconsidering the odds ratio as a measure of 2 × 2 association in a population. Statistics in Medicine 2004; 23(2): 257–270.
- 20 Walter SD. Choice of effect measure for epidemiological data. Journal of Clinical Epidemiology 2000; 53: 931–939.
- 21 Kraemer HC, Kazdin AE, Offord DR, Kessler RC, Jensen PS, Kupfer DJ. Measuring the potency of a risk factor for clinical or policy significance. Psychological Methods 1999; 4(3): 257–271.
- 22 Sackett DL. Down with odds ratios! Evidence-Based Medicine 1996; 1: 164–166.
- 23 Kraemer HC. Correlation coefficients in medical research: from product moment correlation to the odds ratio. Statistical Methods in Medical Research 2007; 15(6): 525–545.
- 24 Rothman KJ, Greenland S. Modern Epidemiology. Lippincott Williams & Wilkins: Philadelphia, 1998.
- 25 Cohen J. Statistical Power Analysis for the Behavioral Sciences. Lawrence Erlbaum Associates: Hillsdale, NJ, 1988.
10.1046/j.1526-4610.2001.111006343.x Google Scholar
- 26 Kraemer HC, Kupfer DJ. Size of treatment effects and their importance to clinical research and practice. Biological Psychiatry 2006; 59(11): 990–996.
- 27 Acion L, Peterson JJ, Temple S, Arndt S. Probabilistic index: an intuitive non-parametric approach to measuring the size of treatment effects. Statistics in Medicine 2006; 25(4): 591–602.
- 28 Grissom RJ. Probability of the superior outcome of one treatment over another. Journal of Applied Psychology 1994; 79: 314–316.
- 29 McGraw KO, Wong SP. A common language effect size statistic. Psychological Bulletin 1992; 111: 361–365.
- 30 Murray DM. Design and Analysis of Group-Randomized Trials. Oxford University Press: New York, 1998.
- 31 Singer JD, Willett JB. It's about time: using discrete-time survival analysis to study duration and the timing of events. Journal of Educational Statistics 1993; 18(2): 155–195.
- 32 Kraemer HC, Kiernan M, Essex MJ, Kupfer DJ. Howand why criteria defining moderators and mediators differ between the Baron & Kenny and MacArthur approaches. Health Psychology 2008; 27(Suppl. 2): S101–S108.
- 33 Kraemer HC, Frank E, Kupfer DJ. Moderators of treatment outcomes: clinical, research, and policy importance. Journal of the American Medical Association 2006; 296(10): 1–4.
- 34 Stampfer MJ, Willett WC, Colditz GA, Rosner B, Speizer FE, Hennekens CH. A prospective study of postmenopausal estrogen therapy and coronary heart disease. The New England Journal of Medicine 1985; 313: 1044–1049.
- 35 Writing Group for the Women's Health Initiative Investigators. Principal results from the Women's Health Initiative randomized controlled trial. Journal of the American Medical Association 2002; 288(3): 321–333.
- 36 Wilson PW, Garrison RJ, Castelli WP. Postmenopausal estrogen use, cigarette smoking, and cardiovascular morbidity in women over 50. The Framingham Study. New England Journal of Medicine 1985; 313(17): 1038–1043.
- 37 Bailar JC. When research results are in conflict. New England Journal of Medicine 1985; 313(17): 1080–1081.
- 38 Stampfer MJ, Colditz GA, Willett WC, Manson JE, Rosner B, Speizer FE et al. Postmenopausal estrogen therapy and cardiovascular disease. Ten-year follow-up from the nurses' health study. New England Journal of Medicine 1991; 325(11): 756–762.
- 39 Grodstein F, Manson JE, Stampfer MJ. Hormone therapy and coronary heart disease: the role of time since menopause and age at hormone initiation. Journal of Women's Health 2006; 15: 35–44.
- 40 Jemal A, Ward E, Thun MJ. Recent trends in breast cancer indicence rates by age and tumor characteristics among U.S. women. Breast Cancer Research 2007; 9(3): R28.
- 41 Kaplan EL, Meier P. Nonparametric estimation from incomplete observations. Journal of the American Statistical Association 1958; 53: 457–481, 562–563.
- 42 Breslow NE. Analysis of survival data under the proportional hazards model. International Statistical Reviews 1975; 43: 45–58.
- 43 Appleton DR. What do we mean by a statistical model? Statistics in Medicine 1995; 14: 185–197.