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Credible sources are also characterized by recency, or timeliness. Generally, because many aspects of life change constantly, newer evidence is more reliable than older evidence. For instance, in January 2013, Google’s influenza tracker predicted that 2012–13 would be the worst flu season in six years. (Google uses a model that estimates flu cases based on the frequency of searches for terms related to the flu).⁸ A month later, more precise estimates by the Centers for Disease Control and Prevention revealed that about 6 percent of the U.S. population had contracted the flu during the peak season, only about half of the 11 percent estimated by Google.⁹ In general, if you have a choice between pieces of evidence from two equally credible sources—one from three months ago, the other from several years ago—you should select the more recent evidence.

Of course, some evidence is classic and endures to this day. For example, though the teachings of Confucius are ancient, they command more respect today than the precepts of many contemporary philosophers. And the ideas of Machiavelli are still pertinent to the subject of international relations, even though they are almost five hundred years old. To decide whether evidence is outdated, ask yourself, “Has the claim made by my source become doubtful or false because of changing circumstances since the claim was made?”

With these criteria for source credibility in mind, let’s now look closely at three major strategies for researching your speech: using a library, searching the Internet, and interviewing experts in your topic.