Question to the Department of Health and Social Care:

To ask Her Majesty's Government what is the area under the receiver operating characteristic curve for (1) the NHSX COVID-19 contact tracing application, and (2) the new contact tracing application currently under development that uses the Google and Apple exposure notification application programming interface.

The area under the receiver operating characteristic (AUC) is a value between 0 and 1 which allows for a comparative analysis of different classification systems. In the context of a contact tracing app, it is the probability that the app is able to correctly discriminate between risky and non-risky encounters where an encounter is classed as being with a user that has tested positive for COVID-19.

AUC values are based on modelling assumptions and, due to practical experimental limitations, are subject to uncertainty. A value of greater than 0.8 is generally considered by the scientific community to be ‘good or excellent’.

The new NHS Test and Trace app is estimated to have an AUC which improves on that achieved for the original NHSX COVID-19 contact tracing app and, with the implementation of further enhancements to the risk calculation and the underlying technology provided by Google and Apple, will have an AUC that would be considered good or excellent.