Risk Model of German Corona Warning App - Reloaded

TL;DR

This paper critically examines the risk model of the German Corona Warning App, revealing it relies on a simplistic parameter that underestimates risk, potentially misleading users and emphasizing testing and vaccination instead.

Contribution

It provides a detailed critique of the CWA's risk model, highlighting its limitations and recommending alternative approaches for effective risk assessment.

Findings

CWA uses only one parameter: weighted exposure time.

The model significantly underestimates actual risk.

Users may be wrongly reassured by CWA results.

Abstract

In this paper we discuss the risk model of the German Corona Warning App (CWA) in two versions. Both are based on a general semi-quantitative risk approach that is not state of the art anymore and for some application domains even deprecated. However, it turns out that the CWA uses a much more limited model, that does not even assess risk, but relies only on one parameter, a weighted exposure time. It is shown that the CWA grossly underestimates even this parameter and so may reassure the users wrongly. As the CWA also has other systematic limitations and shortcomings it is advised not to rely on its results but rather on Covid testing and vaccination.