At the beginning of the year, we asked ProPublica Illinois readers what they wanted to know about how we do our work. Thoughtful, challenging questions have been rolling in ever since, and we’ve been answering them in an occasional series of columns. In this dispatch, ProPublica Illinois reporter Duaa Eldeib answers a question about fact-checking in the internet age.

Back in the 1980s, I spent just a couple of years in the newsroom of a small daily paper with a good reputation ... right before it was acquired and downsized to a rag weekly (sigh). In those days we did fact-checking via published sources — which were still pretty much books and newspapers, almost entirely hard copy. Nowadays those same sources appear to be chiefly internet based, with links that can disappear and text that can be changed after it’s been quoted. How do you navigate that? —Maggie Beaumont

When my friends tell me stories that sound too good to be true, I do what’s in every reporter’s DNA: I ask what their source is for the information. Knowing the source helps me judge the truth of what they’re saying, and whether I should believe, say, that it’s illegal to sell Irish butter in Wisconsin. (Pretty much true until last year, when butter lovers went to court.) The same goes for any story we report. Before we include a fact or a statement, we have to ensure it is correct and the source is credible — even if it takes weeks or months to do so.

Ms. Beaumont is right. Back in the day, reporters used books and other paper documents to check their facts. You confirmed Pulaski was a road, not a street, on a paper map. You pored over the city of Chicago’s budget to determine what the Police Department was slated to spend on overtime. You called the Illinois Department of Financial and Professional Regulation to check if a doctor had a disciplinary record.

The sources haven’t changed that much, but how we access them has. Now, in many cases, we can turn to the internet. Not Wikipedia, of course, since it’s not a primary source and people can edit errors into entries. I’ve used the state’s online professional license lookup on a number of occasions. I am frequently on the Illinois Department of Corrections’ website. Its offender search gives me basic information on individual inmates, and its dataset on the state’s prison population provides a broader overview.

I used to have to file Freedom of Information Act requests to obtain state employee salaries, but now the Illinois comptroller’s office provides that information on its website. The city of Chicago has a data portal with information on building permits, crime and city contracts, among many other categories of data.

The internet has been a boon to fact-checking in other ways as well. Reporters can access more information than was available in the past, and faster, too. We still have to make judgment calls on that information, though. Several online tools help. One, the Wayback Machine, archives websites so they never really disappear. Another, reverse image searches, allow us to check if a photo has been manipulated and see where it has been published. And geolocation uses GPS data to access information on an online post. ProPublica even runs Politwoops, a site that stores deleted tweets by public officials.

The BBC’s reporting on a viral video of two women and two *****ren being shot to death by soldiers in Cameroon is a stunning example of just how much technology has improved fact-checking and why it’s so important. Reporters were able to refute claims by the Cameroonian government, which initially dismissed the video as “an unfortunate attempt to distort actual facts.” Seven members of the Cameroonian military were ultimately arrested.

It also highlights the value of being transparent with our readers. We try, whenever possible, to explain the reporting and fact-checking process. We want readers to know the source of information so they can evaluate each sentence or information point. So we sometimes include a piece like this on how we analyzed the data.

And we attribute facts and statements in the story itself. Attribution is a core journalistic principle, said Jeff Sonderman, deputy executive director of the American Press Institute, an educational nonprofit that runs a fact-checking and accountability journalism project. In the digital age, linking to documents so readers can see the sourcing takes that practice one step further.

“It’s reasonable in a very messy information environment for consumers to be discerning, to ask for a certain amount of transparency and disclosure about the quality of each source, and for news organizations that are reputable to be expected to provide that,” Sonderman said. “If we all live up to that, it becomes easier for consumers to sort out the things that aren’t reputable because they are not rising to the same standards.”