Ultimately, doing the same calculation for the other recent long-term trials would then suggest that the addition of selexipag might be associated with the lowest NNT among the evaluated therapies (table 1). So you may find that you’re unable to leave a comment on an article that is more than a few months old. We”re also concerned about anonymous comments. This may contribute to the inhomogeneous decline in event-free survival on Kaplan–Meier curves (arrows) and the distorted number needed to treat calculations when estimated at a specific time of follow-up. This question is for testing whether or not you are a human visitor and to prevent automated spam submissions. The NNT and RR reduction are time-dependent measures, both decreasing with longer follow-up when relative and absolute risk reductions are constant over time, respectively. Absolute risk reduction(ARR) is the difference in event rates between two interventions. More importantly, physicians often make the mistake of trying to intrapolate or even to extrapolate beyond the original study duration to standardise comparisons between interventions. This number is often very different from the relative risk reduction . https://www.healthnewsreview.org/2020/12/reflections-on-2020-you-cant-mask-this-reality/, “The distinction between what we do know and what we do not yet understand should be explained more often and more clearly in our coverage,” said @garyschwitzer. The ideal NNT would be 1, where all the patients in the treatment group have benefitted, but no one has in the control arm. Outcomes overlooked by the NNT and RRs: treatment impact or utility. Absolute risk reduction (ARR; risk difference) Description: the difference in risk between the exposure group after an intervention and the risk in the nonexposure group (e.g., risk of death) Aim: to show the risk without treatment as well as the risk reduction associated with treatment; Usage: cohort studies and cross-sectional studies The problem doesn’t end there, though. Throughout the past 20 years, numerous specific pharmacological agents, including phosphodiesterase-5 inhibitors, endothelin receptor antagonists, prostaglandins, soluble guanylate cyclase stimulators and, more recently, selective prostacyclin receptor agonists have emerged for the treatment of pulmonary arterial hypertension (PAH) [1]. The interpretation of each is presented in plain English rather than in technical language. Herein, we expand on some of these issues raised by the interpretation of our recent meta-analyses on combination therapies in PAH [4, 10] and discuss the calculation and the interpretation of risk reduction and the NNT in the context of the changing landscape of clinical trials in pulmonary arterial hypertension. Value Health. “The absolute risk looks small, so it gets used for the side effects,” said Harding’s head research scientist, Mirjam Jenny. The 20% seems to be a mistake. After conferring with our reviewers, we agree that the absolute difference between the two arms is 0.06% which can be expressed as a 10.5% relative risk reduction or an 11.7% relative risk increase. In the example above, the incidence rates of the primary outcome would be 0.120 versus 0.235 events per person-years, yielding an NNT=1/(0.235–0.120)=8.7≈9 per person-years. This concept is important in the PAH field, which witnessed a progressive shift in study design and duration. Why? In this case, the comparison of the absolute benefits (reduced cardiovascular events) of 6/10,000 to the harms (bleeds) of 3/10,000 is much more informative than to say there was a 10% reduction in events and a 43% increase in bleeds. Interpretation: Among smokers there were 32 excess cases of respiratory disease per 100 smokers during the 18 year study. of a STAT story on new aspirin guidelines, we praised them for using both absolute and relative numbers. 12.5.1 Relative and absolute risk reductions. However, many physicians express scepticism when efficacy is presented only as odds or risk ratios (RR) because of the dangers of misinterpreting the importance of a therapy when relying solely on relative effect estimates. At the same time, serious bleeding events increased from 0.07 percent among non-aspirin takers to 0.10 percent among those taking aspirin, or a 40 percent relative increase in risk. The authors of the Retraction Watch comments policy urge commenters: “Shed light, not just heat. Thus, its calculation may lead to misleading interpretations, especially for studies involving varying follow-up times or recurrent outcomes. It’s possible the researcher quoted in the story miscalculated. The number needed to treat (NNT) is an epidemiological measure used in communicating the effectiveness of a health-care intervention, typically a treatment with medication.The NNT is the average number of patients who need to be treated to prevent one additional bad outcome (e.g. Sep-Oct 2002;5(5):431 … Using the same cumulative incidences we can calculate the risk difference, an absolute measure of association. This concept is important in the PAH field, which witnessed a progressive shift in study design and duration. Thomas B. Newman, Charles E. Mcculloch, in Goldman's Cecil Medicine (Twenty Fourth Edition), 2012. We do not capture any email address. My back-of-the-envelope calculations agree with yours. Even respected journals do not make it clear that the findings are relative rather than absolute. At the same time, serious bleeding events increased from 0.07 percent among non-aspirin takers to 0.10 percent among those taking aspirin, or a 40 percent relative increase in risk. However, clinical trials evaluating phosphodiesterase type 5 inhibitors were of shorter duration (31±27 weeks versus 90±56 weeks). Indeed, multiple factors, in addition to the efficacy of the therapy and the comparator, may directly influence the NNT and RR and should be taken into account in their interpretation. Hazard Ratios. In the example above, there is a 5% absolute risk reduction with treatment B if the event rate is 20%. Risk Ratio = CI e /CI u = 0.90/0.58 = 1.55. The absolute risk reduction does not involve an explicit comparison to the control group as in the relative risk reduction and thus, does not confound the effect However, it is a less intuitve measure to interpret. Absolute risk (AR)= number of cases in group / total number of group. Najwa Somani, Marty E. Sawaya, in Comprehensive Dermatologic Drug Therapy (Fourth Edition), 2021. Kaplan–Meier curves for the probability of a first adjudicated primary end-point event in the AMBITION trial, suggesting that the primary outcome events frequently clustered around study visits. Relative risk reduction. So total risk reduction does not provide the info that at what base the risk reduction happened. With reference to the data in Table 1, the absolute risks of sexual dysfunction with venlafaxine However, even with appropriate computation, the comparison of the NNT and RR between therapies is generally misleading unless therapies were tested in similar study populations with the same disease severity, the same outcomes, against the same comparator and over the same time frame. Statistical Interpretation of Data. Hazard Ratios. It is a decimal number although often expressed as percentage. Thus, study duration alone may largely influence differences in RR reduction. RRR= absolute risk reduction divided by the control group risk. Of note, a method for estimating the proportion of patients who benefit from a treatment and its NNT when the outcome is a continuous variable has been suggested [21]. European Respiratory Society442 Glossop RoadSheffield S10 2PXUnited KingdomTel: +44 114 2672860Email: journals@ersnet.org, Print ISSN: 0905-9180 However, even with appropriate computation, the comparison of the NNT and RR between … The journalist would then be able to tell the rest of the story in the article (true value to the consumer). Absolute risk reduction (ARR) = AR in exposed - AR in unexposed. It is an effective way of demonstrating a treatment effect. The risk difference or absolute risk reduction (ARR) is the difference in risk between the groups, defined as earlier. Absolute risk is the size of your own risk. We ask that all commenters leave their full name and provide an actual email address in case we feel we need to contact them. This mismatched framing often gets picked up by journalists who report on the study. a reduction in risk from 4% to 3%). Appropriate use of attributable proportion depends on a single risk factor being responsible for a condition. The ratio of these is the risk ratio, a relative measure of association. However, the Kaplan–Meier approach is also subject to distorted NNT calculation, especially when outcomes of interest do not occur randomly. Conversely, the NNT to “prevent” clinical worsening may be misleading, as the NNT best applies to acute conditions without long-term sequelae. Interpretation of Absolute Measures of Disease Risk in Comparative Research William H. Replogle, PhD; William D. Johnson, PhD Research Series From the Department of Family Medicine (Dr Replogle) and the Depart-ment of Preventive Medicine (Dr Johnson), University of Mississippi Medical Center. We will also end any thread of repetitive comments. But the relative risk reduction formula provides that information also because it allows for the percentage change. More pragmatically, this constant absolute risk reduction after 6–12 months of follow-up questions the requirement for long-term event-driven trials in PAH, especially that morbidity events occurring at 3, 6 and 12 months were recently shown to reliably predict subsequent deaths [19].
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