It’s dated, from 1974, but not a whole lot has changed ever since.
There is a lot of interesting information in this book.
For instance, when you get widely divergent results, it’s probably a result of bilingual learning. Say you speakers of Lect A on nearby Lect B. Suppose the males score 90% and the females score 50%. This is almost always due to bilingual learning. The males have been dealing with Lect B speakers because they leave the village to work and whatnot, whereas the women just stay home and have no exposure to Lect B. So the score is that Lect A has 70% intelligibility of Lect B.
It’s important to test speakers individually. Testing in groups results in cases where a strong personality, often male, may lie and say that he can understand all of the text. Everyone else just agrees with him. The strong personality says this because he thinks it’s insulting to admit that he can’t understand the lect. The others, especially women or weaker men, just go along because he’s a strong personality.
Ability to understand another lect is independent of age, sex, status, income and other variables. That right there is pretty interesting.
Anyway, here is the book for download on this site. It’s over 200 pages, so it’s a mouthful.
- Casad, Eugene H. 1974. Dialect Intelligibility Testing. Summer Institute of Linguistics Publications in Linguistics and Related Fields, 38. Norman: Summer Institute of Linguistics of the University of Oklahoma. xiv, 201 p.