In Where Did You Get This Number? (Simon & Schuster, Aug.), Salvanto, the director of elections and surveys for CBS News, walks readers through the polling process.

Why write the book now?

In a larger sense, it was to give people a way to see how pollsters look at the world. A poll can be a means to an end. What we [pollsters] want to know is who’s out there. Who’s talking with us? Who isn’t? What [are people willing to] share? All of that adds up to where the country is headed. In a more narrow sense, I wrote the book to simply explain how polls work and, frankly, the fact that they still do.

How did the 2016 presidential race affect polling and the public’s opinion of it?

Coming out of 2016, I got a lot of questions about the way polls worked. I also got a lot of questions about the difference between a poll and a prediction. It’s an important distinction. Campaigns are dynamic. They are a process, where people are exchanging ideas, making arguments, and deciding what to do. People should look at polls the same way. One of the lessons of 2016 is to look at a poll and say, that’s now, but what could change?

Has the internet made it harder or easier to conduct polls and surveys?

The challenge is that the internet and social media and all the other ways people are now able to express themselves have become competition for us in a way. Social media has become a counter to the old saw that pollsters used—take our poll to make your voice heard! As a result, we have to not only explain that we’re a scientific survey but make the experience engaging and exciting.

How much competition is there between news outlets to be the first to call an election?

Election nights are really exciting for us. We get to see what the world is revealing in real time. We need to be fast, but we also have to be right. And by “right,” I don’t just mean picking the winner. We also have to offer the right explanation. People know there’s a lot of data out there. They’re interested in it, they’re hungry for it, and they know we have all this information. It’s up to us to communicate the why as much as it is to announce the winner.

Any predictions for the midterm elections?

I’m not making predictions, but at the moment we do see that the House is in play. Remember that these races are contested locally. Watch the number of races that we call “competitive.” Right now that’s around 50. That’s twice the number Democrats need to take back the House. By that measure, it’s a competitive set of races.