Adjustment of threshold values of the SwissCovid App

11.9.2020 – The thresholds values for distance calibration were adjusted for the second time on 11 September 2020. We expect that the effectiveness of the SwissCovid app will improve.

The threshold calibration is used to calculate an infection risk based on the proximity and duration of an encounter. It provides the technical basis for the use of Bluetooth signals to evaluate the distance of 1.5 metres. It is carried out based on the attenuation of the measured Bluetooth signal strength. The threshold values of this attenuation are now increased; the legally defined distance of 1.5 metres relevant for the evaluation remains unchanged.

The reasons for the increase of the threshold values are, on the one hand, findings from new field tests by EPFL and ETH Zurich, which recommend the adjustment. On the other hand, information from users that some expected notifications were not triggered also contributed to this decision. The Federal Data Protection and Information Commissioner (FDPIC) was informed about this technical adjustment and has taken note of it.

With the increase in the threshold values, we expect that the probability of correct notification will increase for persons who have been exposed to a risk of infection. Thus, we expect that the effectiveness of the SwissCovid app will improve.

The recommendations for action in case of notifications by the SwissCovid app about a possible infection with the new coronavirus remain unchanged. An Infection can only be detected by a PCR test for the new coronavirus.

To explain how the threshold value adjustment works and the background of it, we provide a technical explanation for interested laypersons, which can be found under technical information. The document also refers to the scientific paper of the technical universities in Lausanne and Zurich (EPFL and ETH Zurich), which is published on GitHub.

Last modification 15.09.2020

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