Cwa-documentation: Impact of changing transmissionRiskDefaultVector ?

[christianbrb]

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Your Question

I have a question regarding PR https://github.com/corona-warn-app/cwa-app-ios/pull/608

What is the impact of changing the transmissionRiskDefaultVector?

What happens if different keys are associated with different transmissionRiskDefaultVector?

[tkowark]

Thank you for your question @christianbrb ,

we'll move this to the documentation repository as it concerns the general topic of risk assignment to certain keys.

As mentioned in corona-warn-app/cwa-documentation#338, we will soon provide further documentation and especially examples that should make clearer how the assigned default risk per day influence the risk calculation.

The vector just defines the risk associated with a given day starting from the day of the transmitted positive result. Within the 14 days prior to the event, people have different levels of infectiousness, which are reflected by the values within the vector.

[mh-]

@christianbrb If you want to read up more details on this already now, it's explained here: https://github.com/corona-warn-app/cwa-documentation/blob/master/transmission_risk.pdf (case 4 / Figure 14)

[christianbrb]

Hey @tkowark and @mh- :) Thanks for your answers!

Is it an intentional design, that the risk vector is configured within the app? Was there a specific design decision to not configure it centrally within the cwa-server?

It seems to be a very important parameter and it is just controlled by the PR review process. I haven't found test using it.

[mh-]

I haven't found test using it.

Actually, there is one test in the Android App now: https://github.com/corona-warn-app/cwa-app-android/pull/679/files#diff-d64cec3d2ea0a64d0536da01937b6092

[christian-kirschnick]

Is it an intentional design, that the risk vector is configured within the app? Was there a specific design decision to not configure it centrally within the cwa-server?

Yes, it was a conscious decision to not make it part of the app configuration. The app config shall only contain values which are subject to change at some point in time.

The transmission risk vector is sufficiently stable and we do not anticipate any changes there.

[tkowark]

In the meantime we added the example to the risk assessment document, which provides much more detail on how transmission risk levels are applied to the uploaded keys: https://github.com/corona-warn-app/cwa-documentation/blob/master/cwa-risk-assessment.md#an-example

We hope that also clarifies the effects of a changed default vector. If there are further questions, your can of course always open up a follow-up issue.