Over at Microsoft’s fontblog, they discuss linewidth and linespread with regard to the reading speed of a whole damn bunch of volunteers. They cite Miles A. Tinker’s book, Legibility of Print, with some actual quantitative analysis (gasp!) on the quality of various layouts.
I haven’t seen these sorts of numbers before, and I’m happy to see that they reflect what everyone (who knows about this sort of thing) believes: longer lines of text are harder to read, and the distance between lines of text is also important for reading quality. These are the results, which are based upon statistical data, to show people when they want to set 1cm margins on their Word document in order to save paper.
They also say:
In the comments for Typography Tip #3, Adam Twardoch asserts that the line length effects the amount of needed linespacing. Tinker’s data does not back up this assertion. This table shows that 2 points of linespacing performed the best at each line width tested.
Okay, sure, but the numbers also show that for such long line lengths, the reading speed is already shot to hell. No-one is actually suggesting that you can get away with 200mm text blocks if you have a 10pt/20pt typeface, say. (x/y refers to a font size of x and a distance between successive baselines of text of y.) No amount of leading is going to fix that mess.
Going back to that numbers business. It’s great that they’ve nicely tabulated that data for us. But numbers in a table don’t really help to get a good feel of exactly why a 43 pica line with 4pt of extra leading is actually a really bad idea. So I put together a LaTeX document illustrating the 20 different layouts examined; grab it here. The source is also available, in case you’re interested.
On the first page, I’ve put the top five layouts ranked by normalised reading speed. Subsequently, each page is dedicated to a single line width with varying linespreads. The text is chosen arbitrarily from the Edgar Allen Poe story ‘Never bet the devil your head’. Times was selected as the typeface because everyone’s used to it and it shows up bad typography more readily than something a little nicer (in my opinion). I find that this document makes it much easier to get an actual understanding of the results of the cited study.