A friend of mine recently found a stack of newspapers from 1940 hidden away in her basement, so just for fun we read through a few of them. And while it was entertaining to laugh at what we thought were very tame comics and outlandish advertisements, it was especially interesting to read the international news.
The year 1940 was an interesting time in international relations. World War II started a year earlier when Nazi Germany invaded Poland, so there was a lot of coverage of the war in Europe, but at that time Pearl Harbor had not yet been attacked (that wouldn't happen until Dec. 7, 1941), so the U.S. was not officially part of the war.
Seeing these old newspapers reminded me of why date is one key factor in finding credible sources.
We generally consider newspapers to be credible sources for research, and they usually are. But this snapshot of the war, although filled with the most accurate information at the time and meeting all other criteria for credibility, couldn't have served as the only source in a research paper about World War II, because its date meant that it was missing some vital pieces of the puzzle.
If you read only that paper and didn't pay attention to the date, you might think that World War II was still going on. Also, not knowing that the U.S. would later enter the war would certainly prevent you from knowing that it was the U.S.'s bombing of Hiroshima and Nagasaki that eventually ended the war and brought the horror of atomic weapons into light.
Now, this example might seem too obvious—most people with a little bit of familiarity with the war would probably know that there was more to the story, so they'd know to seek out other sources for the research. But date makes a large difference even in contemporary stories. As events unfold over hours, days or weeks, the stories often change a great deal. What a source might contain about a scientific discovery, about a living person, a conflict, a bit of technology or any number of other things can be drastically different if written on a different date.
On the other hand, researching historical events may require that you find primary material to supplement your more current sources, as the facts can get jumbled over time as stories are told and retold.
When doing research, make sure to check the dates of your sources. If you are reading information from a few months ago, use a news search engine to see if there are any new developments. If you are reading a news article about a historic event, look for primary sources from the date of the event to verify the information. Often combining sources from a variety of dates can give you an accurate and complete understanding of your subject.
And for other factors to consider when looking for credible sources, see our Guide to Web Search.