The Economist is a weekly magazine, where articles are never signed by authors. Is it then enough that the magazine itself is in the public domain? I have come across posts like this one stating that individual articles might be further protected under copyright. But if I do not know the author, how can I know?
...articles are never signed by authors. Is it then enough that the magazine itself is in the public domain?
Even though articles are not signed, they are still copyrighted at moment of being written by whoever wrote them, and upon publication by who the authors are writing for. That's basic copyright law; read https://en.wikipedia.org/wiki/Berne_Convention
Further, the magazine's own Terms of Service outlines this:
The contents ... supplied to you in conjunction with the Site and/or a Digital Application (such contents, design and materials being collectively referred to as the "Economist Content"), is copyright of The Economist and its licensors. You may not use or reproduce ... for any reason without written permission from The Economist... http://www.economist.com/legal/terms-of-use
The copyright for articles in The Economist belong to the magazine rather than to the author. They are "work for hire" and the articles are emphatically not in the public domain simply because they were not published under a by-line.
While there is theoretically a possibility that an article could have been in a magazine that did not renew its copyright, but in which an individual did renew his or her copyright, in the case of a major magazine like The Economist, it is exceedingly unlikely that the magazine did not renew its copyright.