Look at the items in the footnotes and bibliography. Valid Most people forget to consider this point. Libraries try to collect a wide variety of material for a wide variety of uses. If you are doing serious research then you need to choose the most authoritative sources available in the library so consider two points. In some magazines the same author who writes this week on AIDS wrote last week on lawn mowers.
Some publications are less reliable, authoritative, and accurate than others.
As one extreme, just think of the supermarket tabloids. While they may have several stories on UFO's they are not likely to be your primary source for a report on extraterrestrial life. By the same token People magazine may have an article on John Kennedy but it is not thorough and analytic enough to serve serious research well. It is almost impossible for anything to be entirely objective. Everyone has, at least, a cultural bias.