I'd love to know how that was determined. Given that:
"If different fonts are best for different people, you might imagine that the solution to the fonts problem would be a preference setting to allow each user to select the font that’s best for them.
This solution will not work, for two reasons. First, previous research on user-interface customization has found that most users don’t use preference settings, but simply make do with the default.
Second, and worse, users don’t know what’s best for them, so they can’t choose the best font, even if they were given the option to customize their fonts. In this study, participants read 14% faster in their fastest font (314 WPM, on average) compared to their most preferred font (275 WPM, on average)"
https://www.nngroup.com/articles/best-font-for-online-readin...
What you actually want to compare speed in the most preferred font to, to show that individual choice is or is not better than one-size-fits-all dictate, is speed in the font that would be chosen as the universal choice by whichever mechanism would be used (to show it is universally better, show that there is no universal font choice that would lead to the average user being faster than with their preferred font.)
All comparing each individual's preferred font to each individual's fastest is showing that an individualized test-based optimized font choice is better for reading speed than individual preference font choice, which I guess is interesting if you are committed to individualized choices, but not if the entire question is whether individual or centralized choices are superior.
The differences between individuals which perform better with different fonts may have nothing to do with the intrinsic qualities of the fonts but may be determined only by the previous experience of the tested subjects with the tested fonts or with other fonts that are very similar to the tested fonts.
Only if you measure reading speed differences between fonts with which the tested subjects are very familiar, e.g. by having read or written a variety of texts for one year or more, you can conclude that the speed differences may be caused by features of the font, and if the optimal fonts are different between users, then this is a real effect.
There are many fonts that have some characters which are not distinctive enough, so they have only subtle differences. When you read texts with such fonts you may confuse such characters frequently and deduce which is the correct character only from the context, causing you to linger over a word, but after reading many texts you may perceive automatically the inconspicuous differences between characters and read them correctly without confusions, at a higher speed.
Many older people, who have read great amounts of printed books, find the serif typefaces more legible, because these have been traditionally preferred in book texts. On the other hand, many younger people, whose reading experience has been provided mainly by computer/phone screens, where sans-serif fonts are preferred because of the low resolution of the screens, find sans-serif fonts more legible. This is clearly caused only by the familiarity with the tested fonts and does not provide information about the intrinsic qualities of the fonts.
Moreover, the resolution of most displays, even that of most 4k monitors, remains much lower than the resolution of printed paper and there are many classic typefaces that are poorly rendered on most computer monitors. To compare the legibility of the typefaces, one should use only very good monitors, so that some typefaces should not be handicapped. Otherwise, one should label the study as a study of the legibility as constrained by a certain display resolution. At low enough display resolutions, the fonts designed especially to avoid confusions between characters, like many of the fonts intended for programming, should outperform any others, while at high display resolutions the results may be very different.
After reading the complete paper, I have seen that the study is much worse than I had supposed based on its abstract.
This study is typical for the font legibility studies made by people without knowledge about typography. I find annoying that such studies are very frequent. Whoever wants to make such a study should consult some specialist before doing another useless study.
The authors claim that a positive feature of their study is the great diversity of fonts that they have tested: 16 fonts.
This claim is very false. All their fonts are just very minor variations derived from 4 or 5 basic types and even those basic types have only few relevant differences from Times New Roman and Arial.
All their fonts do not include any valuable innovation in typeface design made after WWII, and most fonts do not include any valuable innovation made after WWI. They include a geometric sans serif, which is a kind of typeface created after WWI, but this kind of typefaces is intended for packaging and advertising, not for bulk text, so its inclusion has little importance for a legibility test.
I would classify all their 16 typefaces as "typefaces that suck badly" from the PoV of legibility and I would never use any of them in my documents.
Obviously, other people may not agree with my opinion, but they should be first exposed to more varied kinds of typefaces, before forming an opinion about what they prefer, and not only to the low-diversity typefaces bundled with Windows.
After WWII, even if the (bad in my opinion) sans-serif typefaces similar to Helvetica/Arial have remained the most widespread, which have too simplified letter shapes, so that many letters are ambiguous, there have appeared also other kinds of sans-serif typefaces, which combine some of the features of older sans-serif typefaces with some of the features of serif typefaces.
In my opinion, such hybrid typefaces (e.g. Palatino Sans, Optima Nova, FF Meta, TheSans, Trajan Sans) are better than both the classic serif typefaces and the classic sans-serif typefaces.
The purpose of that research study wasn't to survey the entire history of sans-serif design(!), it was to answer a fairly focused question: does OpenDyslexic improve reading for the population it claims(or claimed) to help?
The answer appears to be no.
I'm afraid I assumed this particular part was a joke, but having read it several times I'm no longer sure ...
Assuming it's not a joke, what would you suggest to readers of content using any particular font who don't have "very good monitors"? What are they supposed to do instead? Not attempt to read the content? Save up for a better monitor?