The sky has its limits in covid-19 testing

Research output: Contribution to journalArticlepeer-review


At the time of writing, in July 2020, the COVID-19 pandemic has already inflicted dramatic international restrictions, including airports closing and limiting international travel. It has been suggested that re-opening of airports should involve and even rely on testing travelers for COVID-19. This paper discusses the methodology of estimating the detection and diagnostic accuracy of COVID-19 tests. It explains the clear distinction between the technical characteristics of the tests, the detection measures, and the diagnostic measures that have clinical and public health implications. It demonstrates the importance of the prevalence of COVID-19 in terms of determining the ability of a test to yield a diagnosis. We explain the methodology of evaluating diagnostic tests, using the predictive summary index (PSI), and the minimum number of tests that need to be performed in order to correctly diagnose one person, which is estimated by 1/PSI. In a population with low prevalence, even a high-sensitivity test may lead to a high percentage of false positive diagnoses, resulting in the need for multiple high-cost tests to achieve a correct diagnosis. Thus, basing a policy for opening airports on diagnostic testing, even with the best test for COVID-19, has some limits.

Original languageEnglish
Article numbere0020
JournalRambam Maimonides Medical Journal
Issue number3
StatePublished - Jul 2020

Bibliographical note

Funding Information:
Citation: Linn S, Tzafrir S, Gueron S. The Sky Has Its Limits in COVID-19 Testing. Rambam Maimonides Med J 2020;11 (3):e0020. doi:10.5041/RMMJ.10412 Copyright: © 2020 Linn et al. This is an open-access article. All its content, except where otherwise noted, is distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Acknowledgement: This research was partly supported by the Israel Science Foundation (grant No. 3380/19) and the Center for Cyber Law and Policy at the University of Haifa, in conjunction with the Israel National Cyber Directorate in the Prime Minister’s Office.

Publisher Copyright:
© 2020 Linn et al.


  • Bayes' theorem
  • COVID-19
  • Diagnostic tests
  • Epidemiology
  • Flights
  • Methods
  • Screening

ASJC Scopus subject areas

  • Medicine (all)


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