Line length studies?

[geoff-h -at- MTL -dot- FERIC -dot- CA]

 In the summarized discussion of "optimal" page sizes, a few
 contributors mentioned studies that suggested an optimal
 line length of between 2 and 3 "alphabets" long (roughly 52
 to 78 characters).

 I can't dispute the validity of these studies, as I haven't
 read them, but the conclusion seems dubious and the metric
 seems to be imprecise at best. The conclusion ignores far
 too many sources of variation for me to be comfortable with
 it as a blanket rule of thumb. Four examples off the top of
 my head:

 - The letters of the alphabet differ greatly in width;
 since some letters are far more common than others, using
 all 26 in a single metric doesn't account for these
 variations in usage frequency.

 - Proportional and nonproportional fonts (as opposed to
 "typefaces") differ markedly in their spacing
 characteristics. The proposed metric might work just fine
 for Courier, but probably not for Times and Helvetica.

 - Typefaces vary dramatically in their width and height
 characteristics; the width is more important here, though
 the height may well influence leading (see below). As a
 simple and obvious example, consider the difference between
 Helvetica and Helvetica Narrow.

 - The conclusion makes no mention of the effect of leading
 (line spacing), nor of font manipulations (size, style,
 kerning, tracking, wordspacing, justification). Wide lines
 can be acceptable with broad line spacing and unreadable
 with narrow line spacing. The same line of text will have
 dramatically different widths depending on how you kern,
 track, and justify the type, and depending on the
 proportions of italics and bold type within the line.

 Can anyone provide a literature citation for the studies?
 Offhand, I'd have to say that the conclusion is
 overgeneralized, and perhaps even meaningless. Nonetheless,
 I'd like to critique the studies based on the actual
 methodology and the actual conclusion, not based on a "that
 doesn't sound right" reaction. (Among other things, the
 results of studies often get misquoted or misapplied, and
 the misquotes then take on the air of unshakable law.)

 --Geoff Hart    @8^{)}
 geoff-h -at- mtl -dot- feric -dot- ca

 Disclaimer: If I didn't commit it in print in one of our
 reports, it don't represent FERIC's opinion.