# Technical Details

## Confidence Interval

Many of the estimates on this site come with with a Confidence Interval (CI). The standard Confidence Interval on this site is 5% to 95%. To see the CI for a particular estimate just hover your mouse/finger over the estimate.

## Conditional Immunity

The Immunity is estimated using the technique described in this technical note.

## Infection Detection Ratio

The Infection Detection Ratio is the ratio of the number of detected infections divided by the number of actual infections. It ranges from 0 to 1. The method to calculate it is described in this paper.

## Free Infected Individuals (FII)

The number of Free Infected Individuals estimated using the technique described in this technical note.

## Total Infected Individuals

Total Infected Individuals (TII ppm) is the sum of the Free Infected individual and the known Infected individuals per million of population.

## Currently Infected

Currently Infected refers to known cases who are still infected.

## Years to Herd Immunity

Based on a detailed analysis we consider that countries are able to maintain an effective value of R of about 1.25 without a lock down. This value of R corresponds to herd immunity being reached when 20% of the country have been infected or recovered.

If a country has not reached herd immunity, then the Years to Herd Immunity is calculated by averaging the last ten days of new cases and then using that average incidence to estimate how long it will take, in years, to reach conditional herd immunity. If a country has passed conditional herd immunity, the algorithm looks back at the case history and works out on what day that immunity was achieved, and then works out how long ago that was in years. If the country has passed conditional immunity, the Years to Herd Immunity is presented as a negative number.

## Reproduction Number

The Time Varying are is an estimate of R, the reproduction number, using the R language EpiEstim package. The method was **parametric_si** and the **mean_si** was 4.8 with a **std_si** of 2.3. The mean and std were derived from this paper.