Covid-19, Data and Analytics, Detection and Diagnostics

Challenges of Interpreting Test Results and Implications for COVID-19


Diagnostic tests are a critical tool to contain epidemics, to support medical care, and for public health measures. Understanding when they are accurate and inaccurate is necessary for understanding which individuals have the virus, need isolation, and need their contacts traced.

Many diagnostic tests are reliable, though all are imperfect. And at a large scale, tiny errors in accuracy for single tests can aggregate into large errors if deployed without care. This is especially true when the rate of true infection in the tested population is expected to be low. For example, when testing for infection in a person who doesn’t have symptoms or a history of exposure, or when testing for a history of infection when the overall prevalence of disease for a given population is low.

This paper covers:

  • The accuracy and errors in diagnostic tests
  • How low disease prevalence can cause many false positives
  • Diagnostic testing in normal times: testing for influenza
  • Balancing errors with diagnostic needs
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