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Number Needed to Detect

Nuances in the Use of a Simple and Intuitive Signal Detection Metric

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Data mining algorithms are increasingly being used to support the process of signal detection and evaluation in pharmacovigilance. Published data mining exercises formulated within a screening paradigm typically calculate classical performance indicators such as sensitivity, specificity, predictive value and receiver operator characteristic curves. Extrapolating signal detection performance from these isolated data mining exercises to performance in real-world pharmacovigilance scenarios is complicated by numerous factors and some published exercises may promote an inappropriate and exclusive focus on only one aspect of performance. In this article, we discuss a variation on positive predictive value that we call the ‘number needed to detect’ that provides a simple and intuitive screening metric that might usefully supplement the usual presentations of data mining performance. We use a series of figures to demonstrate the nature and application of this metric, and selected adaptive variations. Even with simple and intuitive metrics, precisely quantifying the performance of contemporary data mining algorithms in pharmacovigilance is complicated by the complexity of the phenomena under surveillance and the manner in which the data are recorded in spontaneous reporting systems.

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The views expressed in this paper are those of the authors and not necessarily the official view of the European Medicines Agency. No sources of funding were used to assist in the preparation of this review. The authors have no conflicts of interest that are directly relevant to the content of this review. The authors would like to thank the following individuals who generously shared their time in reviewing early versions of this manuscript and providing thoughtful insights: Alan Hochberg, Jeffrey Aronson, David Goldsmith, David Madigan and Panos Tsintis.

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Correspondence to Dr Manfred Hauben.

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Hauben, M., Vogel, U. & Maignen, F. Number Needed to Detect. Pharm Med 22, 13–22 (2008).

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  • Data Mining Algorithm
  • Spontaneous Reporting System
  • Credible Signal
  • Classifier Efficiency
  • Disproportionate Reporting