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ukhsa-collaboration / covid19-app-system-public

COVID19 app backend
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No keys from before 2 days prior to onset of symptoms #9

Closed mhoehle closed 3 years ago

mhoehle commented 4 years ago

Describe the bug In TransmissionRiskLevelApplier.kt I see the following:

// COV-3804: We don't want keys from before 2 days prior to onset of symptoms
private const val PRIOR_DAYS_THRESHOLD = -2

Is this choice of -2 days in sync with the corrected version of He et al. (2020) ?

Expected behavior In their recommendation they write: Therefore, from a contact-tracing viewpoint, it may be adequate to enquire about close contacts up to 3 days before the index first shows symptoms. So

private const val PRIOR_DAYS_THRESHOLD = -3

seems a more natural choice? Or how is the -2 motivated?

ChrisJBurns commented 4 years ago

I think this is one of the biggest worries about the app. Many people are concerned that they get told to self-isolate on "arbitrary" figures. So a decision on this should not be taken lightly :+1:

nhs-covid19 commented 3 years ago

Thanks for your interest in the NHS Covid-19 project. We are working closely with a number of research organisations, as well as with Apple and Google on the development of their APIs, and the correct risk parameters to apply. The parameterisation of any API calls represents the best available advice at the time, and will be updated as and when this advice is updated.

mhoehle commented 3 years ago

Thank you for the reply, which unfortunately provides little information.

Could you as part of your transparency effort please provide 1-2 references/sources which the choice of -2 days is based on?