When Google recently silently made Chrome log you in whether you logged yourself in or not, I switched to a different (previously unused, non-Chrome) browser on a new computer, and without logging in to anything Google (but from the same house), I went to YouTube. It asked me to log in, but I didn't. It proceeded to suggest mainly links to very niche-interest, low-view-count videos I had previously in the past few days, making it clear that it had at least a very good guess who I was anyway.
Apparently, asking me to log in was mostly just asking for my permission for what they were going to do whether I agreed or not.
You're making the assertion. Do you have evidence to dispute the DDG study? The onus is on you.
In other words, the study proves that different people get different results. It doesn't prove, as they claim in some press, that this is because Google tracks you while you aren't logged in. It's misleading on DDGs part to claim such of that's the case.
(I work at Google, but have nothing to do with ads).
As a broader point, just because you have a null hypithesis does not mean the study is biased. That's completely not how academia works.
Bias as the gp used it doesn't mean statistical bias which also isn't what you mean, but more like "even if these results are technically accurate, they may be misleading", a common example would be p-hacked results. This, contrary to what you say, often involves inventing a hypothesis after the fact, such that it is easily disproven with your data.
However, there isn't evidence that this was what was happening, and Google hasn't exactly covered itself in glory on the privacy front so I tend not to give them the benefit of the doubt on this front. I'd love to see a response from them addressing some of the points from the DDG study.
I don't believe that Google tracks you in incognito mode. My understanding that the DDG study showed that they continue to track you when not logged in, which is consistent with Google's public statements on the matter.
Their methodology was pretty flawed and to top it all they also results "positive" to this kind of analysis.
This does not implies that google does not track incognito users either.
That said, I think the DNT flag being formalized is important to web development.
Previously, one of the core arguments of advertisers was "people do not care about being tracked". Individuals choosing to turn on DNT demolishes that.
Unfortunately, browsers turning it on by default muddles that indicator or intent, even if it's good for individuals.
No browser ever expected it to do anything other than provide additional tracking metadata.