Accuracy is very important, especially in non-fiction writing, so making sure your facts and figures are correct is vital.
Fact-checking does not just mean making sure every statistic or nugget of information in your book is correct, it is also about checking the spelling of names, places and titles.
You would be surprised how many times you think you know how something is spelt and then you check it and find you were wrong. Spiderman once tripped me up, I was sure it was spelt as one word but when I checked with Marvel I saw it is actually Spider-Man – and this reminds me to check EVERYTHING even if I think I know how to spell it!
To check spellings the best way is to copy the word from your manuscript and paste it into Google (that way you can ensure you are not entering a different spelling from the one in your text). Generally there will be a consensus on a spelling but some names, especially those translated from a different script can have a number of spellings and the best bet is to go with the spelling used by an august institution or trusted source such as the BBC.
For facts, such as statistics, the best way to confirm them is to go right back to the source of the data. Ignore articles that are regurgitating the information and find the actual press release or dataset from the source of the information to confirm you have the correct numbers.
If you are publishing any tables or graphs I find it helps to print out my version and the source and then tick each correct figure against the source – sometimes looking at these things on paper is easier than on screen and by keeping the print-outs you can easily go back and reassure yourself you have accurate data.
If you are checking dates, such as birth and death dates, again the Internet is the quickest method. Put the dates and name into Google and then make sure what you have is agreed by at least three reliable sources (Wikipedia does not count I’m afraid). Reliable sources mean organisations and institutions, scholarly articles, reliable encyclopedias such as Britannica and quality newspapers.
If you come across a lovely fact you are desperate to use but cannot find a second source you can still use the fact as long as you qualify it by noting in your work where you found it and that it is unverified.
The problem with fact-checking is that sometimes you just have to take a position because there can be debate over the exact spelling of a name or the location of somebody’s birth. In this case it is worth noting in your introduction that you have gone to every effort to ensure accuracy but that some facts included therein may be open to dispute.
Errors can creep in but to feel confident you are producing the most accurate work you can the best advice I can give is to check everything, even things you think you know, because you would be surprised how often this sieves out errors.