Ideally you will have checked all your facts before you started writing. But when making a fact-checking editing pass, you can double-check. We leave this pass until after we’ve edited for voice, because in that pass we may have changed enough of the wording to require a second look at the factuality of our statements.
☐ The facts employed are credible and enhance the purpose or story.
When I say “credible” what I mean is that the fact or statistic is presented in a way that encourages the reader to believe the author has really done their homework. Here’s a noncredible way of presenting a “fact” about divorce:
It’s well known that half of all marriages end in divorce.
Simply stating that something is “well known” is not a citation. Plenty of “well known” things prove to be untrue. Here’s the credible way to present the same fact:
Data from National Vital Statistics System shows that in 2012, the most recent year for which statistics are available, the U.S. marriage rate was 6.8 per 1,000 people, while the divorce rate was 3.4 per 1,000 people. That’s down from a divorce rate of 3.7 in 2002.
The goal is to get to a primary source—an agency or researcher that has collected direct and specific information about the subject.
If a fact like this is included in your book, it should support your purpose, and not merely be thrown in to pad your word count or because while looking for one thing you came across something else that was interesting. Those kind of findings make for good blog posts, but they don’t necessarily belong in your book unless they support your theme or premise. Especially in prescriptive nonfiction, we don’t want to distract the reader with irrelevant data.
☐ Sufficient support is given where needed.
I have seen manuscripts and even published books where statistics are thrown in or alluded to without back up. Or if support is given, it’s insufficient—say, a Wikipedia citation. Don’t use Wikipedia for anything you’re going to stake your reputation on.
Besides, quoting from Wikipedia, even with attribution, is a bad idea not only because is it notoriously unreliable, but because their copyright policy is so strange. Wikipedia’s copyright notice says each article’s copyright belongs to its authors, but any article may have multiple authors.
One thing Wikipedia is good for is giving yourself background information about a subject you are unfamiliar with. At the bottom of each article is a list of “External Links” that will usually be authoritative. Use those sources.
Providing credible data and sufficient support means going to primary sources for your information as much as possible. Use Encyclopedia Britannica or another respectable, vetted secondary source if you must (use your local library if you don’t want to pay for a Britannica subscription). But the more you use primary sources, the better. Best of all is when you are the primary source.