### Estimates and techniques

The following parameters are estimated per country (or geographical area):

**Cases infected:**Prevalence of COVID-19, i.e., (fraction of) the population that has been infected of COVID-19.**Cases daily:**The new population (or the fraction thereof) infected on a particular day (to the available knowledge).**Cases contagious:**The population (or the fraction thereof) that can transmit the COVID-19 on a given day.**Cases active:**The population (or the fraction thereof) that is infected and whose case is still active on a given day. It includes symptomatic and asymptomatic cases.

We use the following techniques to estimate these parameters:

**Confirmed:**These are the values derived from the official data of confirmed cases obtained from the European Centre for Disease Prevention and Control (ECDC). Cases daily are the new cases confirmed in a given day. To estimate cases contagious and active, the distributions of the number of days a case is infectious and active are used, respectively.**cCFR-based:**This technique uses the official data of confirmed cases and fatalities obtained from the ECDC, as described in (1) and (2). It uses a known Case-Fatality Rate and the number of fatalities to correct the number of confirmed cases, taking into account the time from infection to death.**cCFR-Fatalities:**This is similar to cCFR but using only the official number of fatalities. It uses a value of 15 as time from onset to death (source:

Centers for Disease Control and Prevention, CDC).**300Responses:**The 300 most recent responses to the CoronaSurveys survey are used to estimate the country parameters. See (3) below.**W Estimate:**The responses from the latest W days to the CoronaSurveys survey are used to estimate the country parameters.**UMD Symptom Survey Estimated Cases:**The direct symptom responses from the University of Maryland COVID-19 World Symptoms Survey Microdata (part of the CMU/UMD COVID-19 Symptom Survey initiative) are used to estimate the ratio of cases with COVID-like ill (CLI). COVID-like illness: fever, along with cough, shortness of breath, or difficulty breathing.”**UMD Symptom Survey Estimated Indirect Cases:**The indirect responses from the University of Maryland COVID-19 World Symptoms Survey Microdata are used to estimate the the ratio of cases with COVID-like ill (CLI). These are responses to the survey question “How many people do you know with these [CLI] symptoms?.”

**NOTE: Known issues with the information presented that we are in the process of being corrected:**

- The scale with number of cases on the right of the plots is inaccurate. The scale on the left with the percentage of the population is the correct reference.

### World risk map with current estimates of cases

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### Estimates of active cases per country

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### Estimates of cumulative infected cases per country obtained by CoronaSurveys

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### Estimates of cumulative infected cases per country

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### More Data and Estimates

All the collected data and other estimates can be found in the project GitHub repository at https://github.com/GCGImdea/coronasurveys/tree/master/data.

### Data Sources and Computation

Source of data on confirmed cases and deaths: European Centre for Disease Prevention and Control.

(1) CoronaSurveys estimates using the cCFR-based technique described in Section 3.1 of CoronaSurveys: Using Surveys with Indirect Reporting to Estimate the Incidence and Evolution of Epidemics.. Based on Hiroshi Nishiura et al. Early Epidemiological Assessment of the Virulence of Emerging Infectious Diseases: A Case Study of an Influenza Pandemic. Plos One. August 31, 2009. https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0006852.

(2) The ratio of cases contagious and active are estimated as described in Estimating active cases of COVID-19: The unknown matters.

(3) CoronaSurveys estimates using the **Region based approach** (using 300 responses) described in Section 2.2 of CoronaSurveys: Using Surveys with Indirect Reporting to Estimate the Incidence and Evolution of Epidemics.. (CI-L, CI-H) is the 95% confidence interval computed as described there. Corresponds to the latest date with sufficient cumulative number of survey responses. The label “undefined” is used when there are not enough survey responses to compute estimates.

(4) CoronaSurveys estimates using the **Country based approach** (using 30 responses) described in Section 2.2 of CoronaSurveys: Using Surveys with Indirect Reporting to Estimate the Incidence and Evolution of Epidemics.. (CI-L, CI-H) is the 95% confidence interval computed as described there. Corresponds to the latest date with sufficient cumulative number of survey responses. The label “undefined” is used when there are not enough survey responses to compute estimates.