Reading Literature on Screen: A Price for Convenience?

I've often been curious if reading on screen was as valuable as reading a physical page.  I'll be interested in future studies, but I know I read more with my phone and iPad than I would without them. 

She said more research is needed to understand what’s lost by reading literature on screen. She added that the type of text, the device used, and the background experience of the reader could all influence the outcome