It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
In evaluating information the concept of Authority refers to the both the author's and publisher's credibility. Why is/are the author(s) qualified to create this particular information? Why is the publisher credible for this topic?
To help evaluate this:
Look for information about the author within the information itself
Search for examples of other writing by the author
See if the author is cited in other information you have found
Google the author's name to see if you find a resume or CV
Google the publisher to find out their focus (look for "about" statements)
For Letters to the Editor. Click on Advanced Search and change the form from ALL to NEWS. Type Letters in the first box and switch it from All Fields to Section. Type your topic in the second box. Scroll down to click Search.