[oniTony]

That's most of the way there, but if there's sufficient amount of combined traffic, ad hoc reports will start populating from sampled data instead of showing exact results. This might prevent getting any meaningful data about e.g. how A/B test is performing when filtered to a specific segment.

[ApolloRising]

oniTony not sure what you mean exactly since this would just filter traffic to your own domain. This only works moving forward and usually is setup when a profile is created. Filters will not work retroactively with Google Analytics.

Would be happy to discuss if you could clarify your statement regarding A/B testing.

[oniTony]

I went back to the Analytics Admin panel to double check, and it indeed looks like filters are applied to specific views. The tracking code collects data at the property level.

From https://support.google.com/analytics/answer/2637192?hl=en

> If the number of visits/sessions to the property in the given date range exceeds 250K visits/sessions, GA will employ a sampling algorithm...

> It is important to note that session sampling occurs at the property level, not the view level.

So it sounds like reports will sample 250K from total traffic first, and apply the view filter after. This has the potential to be left with reports generated on too small of a sample.