The current popular consensus seems to be that you should switch to winter tires during the winter. In its radical form, this conviction is more like "winter tires are better than all season tires in the winter no matter what" but it also comes in many more gentle flavours. It also of course depends whether we are talking about safety or just the driving comfort.
Regardless of a particular wording and a particular aspect being discussed, I see only anecdotal evidence and common-sense reasoning - no hard evidence. Even here on SE (here, here or here) the answers contain only opinions or anecdotes and no really useful facts.
What I've found is only this ADAC test (I know that they've conducted this test before - IIRC results where very similar) where one of top-shelf winter tires Continental WinterContact TS 860 are compared to all season tires.
The result is in favor of these winter tires but:
1) it's a really small difference between them and some models of all season tires
2) they are even not the best tires for braking on the snow (!)
3) this is only a single test with a small subset of available tires
Are there any more objective comparisons between all season and winter tires? Or perhaps some other non-subjective arguments in favor of switching to winter tires?
To keep the question focused, let's narrow the discussion to subzero temperatures on snow and on plowed roads in temperate continental climate (i.e. northern Asia and United States, southern Canada, and northeastern Europe).