This research is interesting because it's highly relevant given Apple's upcoming changes to tracking consent in iOS 14. Unlike the DNT[0] header Apple are in a position to enforce apps actually respecting the users consent preference, either by technical means or by kicking offending apps off the App Store. The walled garden has many problems but this is one of the benefits. Given that almost all apps and websites have implemented GDPR's consent management in a supremely user hostile way[1] that is far from an equal binary choice I suspect we'll see much higher opt out rates in iOS 14. I've seen people argue that users will just continue to click accept at high rates as they do with current consent management solutions, but I think this is the wrong analysis. Users click accept precisely because the amount of effort required to opt out is unreasonable, when both options require equal effort the number of users clicking accept will plummet.