Abstract
Scientists and policymakers need to compare the incidence of Covid-19 across territories or periods with various levels of testing. Benchmarking based on the increase in total cases or case fatality rates is one way of comparing the evolution of the pandemic across countries or territories and could inform policy decisions about strategies to control coronavirus transmission. However, comparing cases and fatality rates across regions is challenging due to heterogeneity in testing and health systems. We show two complementary ways of benchmarking across territories and in time. First, we used multivariate regressions to estimate the test-elasticity of Covid-19 case incidence. Cases grow less than proportionally with testing when assessing weekly changes or looking across states in the USA. They tend to be proportional or even more than proportional when comparing the month-to-month evolution of an average country in the pandemic. Our results were robust to various model specifications. Second, we decomposed the growth in cases into test growth and positive test ratio growth to intuitively visualize the components of case growth. We hope these results can help support evidence-based decisions by public officials and help the public discussion when comparing across territories and in time.
Highlights
The SARS-CoV-2 pandemic has imposed an enormous global burden, with about 140 million reported cases and 3.0 million deaths in 192 countries and territories, as of April 15, 20211
Limited resources usually mean more stringent inclusion criteria for testing, including, for example, a combination of clinical symptoms and travel history. These restrictive criteria would often result in a higher proportion of positive tests and miss SARS-CoV-2 infections that do not comply with testing requirements
This result suggests that the evolution of Covid-19-case-growth was primarily driven by changes in positive test ratio (PTR) rather than testing
Summary
The SARS-CoV-2 pandemic has imposed an enormous global burden, with about 140 million reported cases and 3.0 million deaths in 192 countries and territories, as of April 15, 20211. Benchmarking may be of limited use because countries or even subnational administrative entities, such as states within the USA, do not have the same testing policies or test availability for SARS-CoV-26 This relation between testing capacity and Covid-19 cases has generated confusion and sparked controversies between experts and public officials in many countries[25,26,27,28,29]. We take a pragmatic approach to suggest two relatively simple ways of comparing total Covid-19 cases and case fatality rates across territories, such as countries or states in the USA, with varying degrees of Covid-19 testing This approach is helpful to benchmark changes over time in a given territory. We hope that our results can help public health officials when they need to benchmark performance over time or vis-á-vis other territories
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