However, these results do not mean much if they are not related to the x-heights. The strength of the relationship between x-height and line spacing is indicated by a correlation coefficient.
A second indication that typographic guidelines and practical documents differ is that the line spacing for type with the same x-height varies considerably.
Unfortunately, it is not possible to relate the actual measures of x-height and line spacing of text to the original point sizes in which a text was specified.
I took the most frequently appearing x-height in my study, 1.60 mm (0.06[inches]), as an example.
Table 1 shows that type with an x-height of 1.60 mm (0.06[inches]) and a line spacing of 4.25 mm (0.167[inches]) could have a body height between 7.1 points (Didot) and 11.4 points (pica).
It might be the case that the range of 1.30 mm to 1.90 mm for the x-height is similar to the range of 8-14 points body height.
Figure 7 shows a scatter plot of the relationship between x-height and line length in 110 novels.
The variation in line length for type with the same x-height is large.
There seem to be distinct boundaries within which document developers of scientific journals, novels, and brochures specify x-height, linespace, and line length.
Other criteria - such as cost, standardization, or production deadlines - might be more influential on typographic decisions about x-height, line spacing, and line length.
Figure 4 shows the x-heights of the documents measured in this study.