I really hesitated to post the link to the line width article because
- It's old - 2002 is old in eTime.
- It's stating CPL which is a print unit of measurement.(So is em but at least em is used as an online measurement and it resizes well).
- It doesn't say what monitor sizes were used at what resolution.
- It doesn't say what colors where used or even if it was white text on black background or black on white (many people "assume" that dark text is best but several informal tests by web designers have shown that preferences are almost evenly split. Does anyone remember using a CRT? They were all light text on dark backgrounds. DOS/Command Prompt still presents white text on a black background)
- It doesn't say what font was used
- It doesn't say what font size is being used
- It doesn't say how many characters were in a paragraph - short or bulleted is best online, not long wordy paragraphs
- It doesn't say what line spacing was used
- It doesn't say what level of language is being used (did they use the same text for young and old? 18 - 61 is too wide of a range to determine *all* preferences. Different decades have different exposure rates to different media.)
- It doesn't say if the study used people who read text on monitors often, or never before. (*I* have never liked print materials with 1 - 1.5" white space on each side but that's been a common format that most generations of people have learned to EXPECT in printed material. Expectations create preferences. I have an impression those types of margins were originally set to make it easy to bind pages together and allow wear from page turning to occur outside the text area. Those aren't issues with online presentations.)