Before I delve into the Internet vs. books debate let me start with one point that I think is overlooked by the slightly narrow scope of the topic. When searching information that is authoritative and accurate primary sources should raise above secondary sources. Primary sources are information that is gleaned directly from the first-person format. These sources are usually memoirs or writings created by an individual who were there at the time.
One of the great things about the Internet is that anyone can bring any content they choose to the masses. The downside is that misinformation is rampant: personal agenda's, political biases, and just plain stupidity can affect the quality of information gleaned from the Internet. So, in general, books from authoritative authors are more likely to provide you with the best information. That does not leave the Internet out of the picture, but you must take care to gather your information carefully. Here are some suggestions to consider:
#1: Formal websites such as the National Institute of Mental Health, or from the Department of Human Health and Services can be considered reliable sources of information.
#2: Google has a separate search engine project named, Google Scholar, that searches peer reviewed journals and other authoritative sites. The problem here is that often the article you want will only be available in its abstract form. You can buy the article or subscribe, at a fairly hefty price, from the journal to get the full text. You can take the information you have found to your local librarian and they may have access to it.
#3: Many colleges and libraries buy subscription packages that allow you access to full text articles from a group of journals. If you are a college student, you may be able to access this service from your home computer with a pass code; otherwise you will have to go to the school or library to do your research.
#4: If your community or college is small, they may have a smaller selection, as these are a significant expenditure for the institution. For example, my local community college cannot get access to full text articles from Nature. Nature is a magazine (and all of their associate magazines) that is coveted by scientists and others. They vie for the opportunity to have their work published there first. Many of the science "blips" on T.V. news are reported shortly after publication in Nature.
Accurate information needs to be gleaned from sources that are reputable. Textbooks, scholarly journals and official government websites rate high on the dependability scale. Other books and Internet sources should be examined carefully. Books often provide a better look at the writer's experience and background through a short biography. Just because it is written down somewhere or posted to a website does not give it automatic authenticity.