Heading Frequency and Comprehension: Studies of Print Versus Online Media 
This paper describes a study that examined the effect of heading frequency on comprehension and perceptions of information presented in print versus online text. Results indicated that heading frequency did not differentially affect the comprehension of readers of print text while it did differentially affect the comprehension of readers of online texts who had considerably lower comprehension scores with text that had high frequency versus medium frequency headings.
Spyridakis, Jan H., Laura D. Schultz and Alexandra L. Bartell. STC Proceedings (2005). Articles>Document Design>Writing>Usability