I don't think you can take away any useful information from this "study". A single glance at the sources is enough to tell you that the author selected a sample that would guarantee them the conclusion they wanted.
All the newspapers in the screenshot are notoriously right wing, as is every other paper that gets mentioned, apart from the Guardian. I guess that one was included to make the biased sample seem less obvious, and since they happen to be quite neutral on Corbyn, so they don't offset the stats too much.
This study is the equivalent of only looking at "Fox News" and other similar news broadcasts, and drawing the conclusion that American media as a whole is very conservative and supportive of Trump.
Hmm, it's perhaps a valid point but as far as I can tell the only English paper missing is The Times (other than small mad ones like the Daily/Morning Star).
I'd take the opposite interpretation. It probably says even more about bias that those are the sources available to choose from (though I'd also say the Mirror is left wing, the Guardian sort of centrist and who knows what's going on with the Independent though in further reduction of the free media pool they've just been bought by a right winger).
I wouldn't call it sampling bias if it reflects the actual existing reality, those are the media sources available (except in Scotland and NI) and they're biased against the opposition.
Aside from all the Times flavours, The Observer and "i" are both left leaning papers that are missing.
Although there are overall probably more left wing than right wing papers among the small ones (like the Daily/Morning Star, as you mentioned), there do seem to be more conservatives newspapers among the big names.
That comes as a bit of a surprise to me, given the situation is the opposite when it comes to non-print media. I struggle to think of a news channel which is obviously conservative. I definitely wouldn't call BBC that, and others like Channel 4 are as openly left-wing.
As someone who predominantly follows television and online news, I haven't personally noticed any conservative bias in the available options, and even a slight under-representation if anything.
Daily Mirror is left-wing as is The Independent. Both are prominently featured in the screen shot, along with the Guardian, which you already mentioned. Either you're very poorly informed about the different papers political leaning, or not very observant.
Also, more of the best-selling papers are right-wing than left, so it's natural there will be more.
http://www.lse.ac.uk/media-and-communications/assets/documen...