Excluding books like novels which are written to be read from beginning to end, the easiest to skim-read books have chapter and section divisions, each with intro and concluding paragraphs. They have pictures, charts, and diagrams; they have margin notes summarizing each paragraph; they have color. Each paragraph has a topic sentence, either first or last. The book begins with contents on a single page, then a detailed contents. The written word's come a long way since scrolls were the writing medium.

I'd say the squint test does apply to the written word.