I'm planning (somewhat technical, but not very technical) undergrad courses in the fall with relatively little lecturing in class, primarily using class time for group work and discussion (as explained in and as a follow-up to: http://academia.stackexchange.com/q/67080/19607).  I'm trying to choose reading material that students are more likely to read. 

> Is there any evidence (preferably actual research, but ancedotal if necessary) that certain "formats" of required reading are more likely to be read by students?  Specifically I have in mind the following tete-a-tete's:

 - physical books versus e-books versus online notes
 - free versus low-priced versus expensive books
 - one long book versus several short books