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Exaggeration of treatment benefits using the "event-based" number needed to treat

Canadian Medical Association journal (CMAJ), 2008-09, Vol.179 (7), p.669-671 [Peer Reviewed Journal]

COPYRIGHT 2008 CMA Impact Inc. ;COPYRIGHT 2008 Joule Inc. ;Copyright Canadian Medical Association Sep 23, 2008 ;2008 Canadian Medical Association ;ISSN: 0820-3946 ;EISSN: 1488-2329 ;DOI: 10.1503/cmaj.080018 ;PMID: 18809898 ;CODEN: CMAJAX

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  • Title:
    Exaggeration of treatment benefits using the "event-based" number needed to treat
  • Author: Aaron, Shawn D ; Fergusson, Dean A
  • Subjects: Analysis ; Care and treatment ; Clinical trials ; Evidence-Based Medicine ; Humans ; Lung diseases, Obstructive ; Medical research ; Medicine, Experimental ; Methods ; Models, Statistical ; Mortality ; Outcome Assessment (Health Care) ; Prevention ; Pulmonary Disease, Chronic Obstructive - drug therapy ; Recurrence ; Risk Assessment ; Risk factors ; Sample Size ; Side effects ; United States
  • Is Part Of: Canadian Medical Association journal (CMAJ), 2008-09, Vol.179 (7), p.669-671
  • Description: Since being introduced into the medical literature in 2005,1 the event-based number needed to treat has been used extensively to describe results of respiratory clinical trials. In a recent clinical trial, Kardos and colleagues found that the rate of exacerbations of chronic obstructive pulmonary disease was 0.92 per patient per year among patients randomly assigned to treatment with fluticasone and salmeterol, and 1.4 per patient per year among those randomly assigned to receive salmeterol. 8 The authors calculated the number needed to treat to be 2.08 (1 ÷ [1.4-0.92]). They therefore stated that the number of patients needed to treat with fluticasone and salmeterol rather than salmeterol alone to prevent 1 exacerbation of chronic obstructive pulmonary disease per year was 2.08. Similarly, the recently published Towards a Revolution in COPD Health (TORCH) trial observed an annual rate of exacerbations of 0.85 in the fluticasone and salmeterol group and 1.13 in the placebo group. The authors calculated a number needed to treat of 4 (1 ÷ [1.13-0.85]), implying that 4 additional patients need to receive fluticasone and salmeterol to prevent 1 exacerbation over 1 year.9 The event-based number needed to treat has also been used to describe the effects of nonpharmacologic interventions for chronic obstructive pulmonary disease, such as nurse-led intermediate care programs for prevention of unscheduled physician visits.10 Consider the example outlined in Table 1 where 10 patients are randomly assigned to placebo for 1 year and 10 patients are assigned to treatment for 1 year. The treatment is designed to prevent exacerbations of chronic obstructive pulmonary disease. In this example, 1 patient in the placebo group experiences a single exacerbation in 1 year, 2 patients experience 6 exacerbations and the remaining patients have none. In total, patients in the placebo group experienced 13 exacerbations over 10 patient-years, or 1.3 exacerbations per patientyear. In contrast, in the treatment group, 1 patient has 3 exacerbations and 1 patient has 5. The remaining patients have none. In total, patients in the treatment group experience 8 exacerbations over 10 patient-years, or 0.8 exacerbations per patient-year. Calculation of the traditional measure of number needed to treat yields a number needed to treat of 10 (1 ÷ [0.3-0.2]). However, the event-based number needed to treat is 2 (1 ÷ [1.3-0.8]). Consider an alternative situation where 10 patients are randomly assigned to receive placebo for 1 year and 10 patients are assigned to receive treatment to prevent exacerbations of chronic obstructive pulmonary disease. In this example, 1 patient in the placebo group experiences a single exacerbation during the 1 year period, 2 patients experience 8 exacerbations and the remaining patients have none. In total, patients in the placebo group have experienced 17 exacerbations over 10 patient-years, or 1.7 exacerbations per patient-year. In contrast, 2 patients in the treatment group each experience 2 exacerbations and the rest have none. In total, patients in the treatment group experience 4 exacerbations over 10 patientyears, or 0.4 exacerbations per patient-year. The event-based number needed to treat in this example is 0.77 (1 ÷ [1.7-0.4]). This suggests that 0.77 patients would have to receive treatment to prevent a single exacerbation. Clearly it is impossible for 0.77 of a patient to receive treatment. Thus, this statistic has no legitimate clinical interpretation. If the number needed to treat of 0.77 is rounded to 1, it implies that treatment is indicated for every patient because treatment would prevent exacerbations for all patients. Review of the actual data indicates that clearly this is not the case, because 70% of patients in this example would not experience any benefit of treatment. Again, the event-based number needed to treat provides misleading information.
  • Publisher: Canada: CMA Impact Inc
  • Language: English
  • Identifier: ISSN: 0820-3946
    EISSN: 1488-2329
    DOI: 10.1503/cmaj.080018
    PMID: 18809898
    CODEN: CMAJAX
  • Source: ProQuest One Psychology
    GFMER Free Medical Journals
    MEDLINE
    PubMed Central
    Alma/SFX Local Collection
    ProQuest Central
    DOAJ Directory of Open Access Journals
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