Three years ago, the Internal Revenue Service sent a letter to people who had paid a fine, known as the individual mandate, for not having health insurance. The letter, which went out to 3.9 million people, detailed how to sign up for health care coverage.

“Marketplace” host Kai Ryssdal recently spoke with Sarah Kliff, an investigative reporter for the New York Times, about how that letter saved lives.

“Those letters did encourage some people to sign up,” Kliff said. “Those letters ended up saving about 700 lives.”

That data comes from a new working paper from the Treasury Department analyzing the effect of the experiment, which happened only because of a budgeting issue that meant the IRS couldn’t send the letter to everyone who had paid the fine (about 600,000 people didn’t receive it).

“They ended up creating the first experimental evidence that we have that health insurance saves lives, almost by accident,” Kliff said.

Click the audio player above to hear the full interview.