Optimal text lenght
The optimal text line length is dependent upon several factors. It is commonly recommended that shorter line lengths (about 11 words) should be used in place of longer, full-screen lengths. This is because longer line lengths require greater lateral eye movements, which make it more likely to loose one's place within the text (Horton, 1989; Mills & Weldon, 1987). It also has been pointed out by Horton (1989) that longer line lengths are more tiring to read. Horton recommends that lines should be limited to lengths of around 40 to 60 characters, which is approximately 11 words per line. A study by Huey (1968) tends to support this in his finding that shorter line lengths or approximately 4" (10 cm) are more accurate on the return sweep than longer line lengths. Moreover, Gregory and Pouton (1970) state that people with poor reading ability performed better when the line length was approximately seven words. This suggests that young readers who have not mastered reading online, as well as readers who have vision deficits, may be most benefited by having shorter line lengths.
As far as reading time, a study by Youngman and Scharff (1999) found that with 0.5 inch margins, the fastest reaction times were for the shorter, 4-inch (10 cm) lengths over the 6- and 8-inch lengths (15 and 20 cm, respectively). The 4-inch lengths were also preferred over the other lengths. However with no margin widths, the 8-inch line lengths had the fastest overall reaction times. A study by Duchnicky and Kolers (1983), found that full screen lengths resulted in 28% faster reading times over lengths of 1/3 of a screen. It was also found that full and 2/3 screen lengths were read significantly faster than the 1/3 screen lengths.
In a recent study by Bernard, Fernandez, and Hull (2002) that compared three links lengths (24.5, 14.5, and 8.5 cm, respectively) for both children and adults supported the finding that shorter line lengths are preferred more than full-screen line lengths. As far as the perception of reading efficiency, the results were mixed. For adults, the Full-length condition was perceived as providing the optimal amount of scrolling in comparison to the two other conditions—presumably because this condition required the least amount of scrolling. The Narrow-length condition was perceived as promoting the highest amount of concentration, while the Medium-length condition was considered to be the most optimally presented length for reading.
Overall these results suggest a trade-off between faster reading times of the longer lengths and a more preferred reading arrangement of the shorter lengths. Possibly the best arrangement is somewhere between the two. More research needs to be done, however.