Abstract
BackgroundThe number needed to treat (NNT) is a well-known effect measure for reporting the results of clinical trials. In the case of time-to-event outcomes, the calculation of NNTs is more difficult than in the case of binary data. The frequency of using NNTs to report results of randomised controlled trials (RCT) investigating time-to-event outcomes and the adequacy of the applied calculation methods are unknown.MethodsWe searched in PubMed for RCTs with parallel group design and individual randomisation, published in four frequently cited journals between 2003 and 2005. We evaluated the type of outcome, the frequency of reporting NNTs with corresponding confidence intervals, and assessed the adequacy of the methods used to calculate NNTs in the case of time-to-event outcomes.ResultsThe search resulted in 734 eligible RCTs. Of these, 373 RCTs investigated time-to-event outcomes and 361 analyzed binary data. In total, 62 articles reported NNTs (34 articles with time-to-event outcomes, 28 articles with binary outcomes). Of the 34 articles reporting NNTs derived from time-to-event outcomes, only 17 applied an appropriate calculation method. Of the 62 articles reporting NNTs, only 21 articles presented corresponding confidence intervals.ConclusionThe NNT is used as effect measure to present the results from RCTs with binary and time-to-event outcomes in the current medical literature. In the case of time-to-event data incorrect methods were frequently applied. Confidence intervals for NNTs were given in one third of the NNT reporting articles only. In summary, there is much room for improvement in the application of NNTs to present results of RCTs, especially where the outcome is time to an event.
Highlights
The number needed to treat (NNT) is a well-known effect measure for reporting the results of clinical trials
Of the 34 articles reporting NNTs derived from time-to-event outcomes, only 17 applied an appropriate calculation method
The NNT is used as effect measure to present the results from randomised controlled trials (RCT) with binary and time-to-event outcomes in the current medical literature
Summary
The number needed to treat (NNT) is a well-known effect measure for reporting the results of clinical trials. The concept of the number needed to treat (NNT) was proposed by Laupacis et al [1] in 1988 to provide clinicians with a useful measure of treatment benefit It represents the average number of patients who must be treated to prevent one adverse outcome within a certain duration of follow-up time, and is calculated by inverting the absolute risk reduction (ARR) [1,2]. In the past years, the number needed to treat has become a well-known effect measure and is conventionally applied in randomised controlled trials (RCTs) with a binary outcome where the duration of follow-up time is fixed and the time to event plays no role or is ignored [12]. In 2001, the explanatory document of the Consolidated Standards of Reporting Trials (CONSORT) statement noted that NNTs could be helpful in expressing results for both binary and survival time data [13]
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