Question: What primary difference was there between the NAAL and Delta study that made comparisons difficult?
Sentence: While a precise comparison between the NAAL and Delta studies is difficult, primarily because of methodological differences, Zoellner et al. suggest that health literacy rates in the Mississippi Delta region are different from the U.S. general population and that they help establish the scope of the problem of health literacy among adults in the Delta region.
Answer in sentence: yes