Editor:
With interest, I read the article by Li et al. [
[1]
] regarding the NNTnet metric to apply the NNT concept to multiple endpoints. The authors claim that they “propose a new metric, the ‘NNT for net effect’ or NNTnet to present the combined benefit and harm effects of an intervention or therapy based on NNT-type information” and that “no studies have explicitly used the NNT information embedded in a net benefit (or harm) approach, which leaves an important research gap between the net benefit (or harm) concept and the NNT application [[1]
].”However, the proposed basic metric NNTnet = 1/ARRnet = 1/(ARR−ARI), where ARR is the absolute risk reduction regarding an endpoint showing benefit and ARI is the absolute risk increase for another endpoint showing harm, has already been proposed by Riegelman and Schroth [
[2]
] more than 25 years ago. Extensions of the basic metric such as incorporation of utilities and timing have also been considered by Riegelman and Schroth [[2]
]. Similar measures have been considered in detail in the benefit-risk analysis literature, including methods for visualization of results and application in regulatory decision-making [3
, 4
, 5
].On the one hand, the combination of benefits and harms regarding multiple endpoints in one metric solves one limitation of the original NNT, namely that it refers only to one single endpoint. On the other hand, the intuitive meaning of the simple NNT is lost if multiple endpoints with incorporation of utilities are combined in one metric with an unclear scale. In addition, it is difficult to derive appropriate confidence intervals for combined NNTnet metrics. Maybe these are reasons why such extensions of the simple NNT are not routinely applied in medical research. However, these issues have already been discussed in the scientific literature [
[6]
].- Bender R.
Number needed to treat: overview.
in: Balakrishnan N. Brandimarte P. Everitt B.S. Molenberghs G. Ruggeri F. Piegorsch W. Wiley StatsRef: statistics reference online. Wiley,
Chichester2017
https://onlinelibrary.wiley.com/doi/abs/10.1002/9781118445112.stat04972.pub2
Date accessed: October 23, 2020
In summary, the NNTnet metric is not new, not intuitive after adjustments for timing and utilities, and currently not routinely applied in medical research.
Supplementary data
- Data Profile
References
- The number needed to treat for net effect (NNTnet) as a metric for measuring combined benefits and harms.J Clin Epidemiol. 2020; 125: 100-107
- Adjusting the number needed to treat: incorporating adjustments for the utility and timing of benefits and harms.Med Decis Making. 1993; 13: 247-252
- Benefit-risk analysis: a brief review and proposed quantitative approaches.Drug Saf. 2003; 26: 853-862
- A unified framework for classification of methods for benefit-risk assessment.Value Health. 2015; 18: 250-259
- A case study using the PrOACT-URL and BRAT frameworks for structured benefit risk assessment.Biom J. 2016; 58: 8-27
- Number needed to treat: overview.in: Balakrishnan N. Brandimarte P. Everitt B.S. Molenberghs G. Ruggeri F. Piegorsch W. Wiley StatsRef: statistics reference online. Wiley, Chichester2017 (Available at)https://onlinelibrary.wiley.com/doi/abs/10.1002/9781118445112.stat04972.pub2Date accessed: October 23, 2020
Article info
Publication history
Published online: October 07, 2020
Footnotes
Conflict of interest statement: The author has no conflict of interest.
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