\[Se=\frac{P\left(T+\mid D+\right)}{P\left(D+\right)},\ Sp=\frac{P\left(T- \mid D-\right)}{P\left(D-\right)}\]
Sensitivity analysis
The performance of EVI depends on the specified case definition (i.e., \(r\)) and the desired accuracy. Ideally, in the presence of historical data, various case definitions and \(r\) values should be explored to identify combinations that provide the optim
The current most serious threat to global health and economy
\cite{Fauci_2020} is the COVID-19 pandemic that begun in China and was first reported to the WHO China Country Office on December 31, 2019
\cite{world2020pneumonia}. Data on the confirmed cases of COVID-19 were retrieved by the
COVID-19 Data Repository, which is maintained by the Center for Systems Science and Engineering (CSSE) at Johns Hopkins University
\cite{Dong2020}. The number of daily confirmed new cases of COVID-19, for each country, from January 22, 2020 until April 13, 2021 were analyzed. Due to unnatural variability in the reported cases between working days and weekends, the 7-day moving average rather than the actually observed cases were analyzed. For the analysis
\(m_{max}\) was restricted to 30 days in order to avoid the effect of potentially higher volatility from previous epidemic waves on the volatility estimates of the most recent data and the predictive ability of
\(EVI\) for upcoming and perhaps milder epidemic waves.
The case definition was an increase in the mean of expected cases, between two consecutive weeks, equal or higher than twenty percent, \(r\ge\frac{1}{1.2}\). For sensitivity analysis, the detection of an increase in the mean of expected cases equal or higher than 50 percent (\(r\ge\frac{1}{1.5}\)) was considered. Data were analyzed separately for each country and for each of the United States of America that had experienced a total number of cases higher than 20,000, until April 13, 2021.
Statistical software
All models were run in R\cite{team2020r} and the packages readxl\cite{wickham2019package}, ggplot2\cite{wickham2011ggplot2}, cowplot\cite{wilke2019package} and readr\cite{wickham2015package} were used.