"When radio ratings got more precise, it changed how programmers saw their audience. Are podcasters heading for something similar?"

NL:

“Some stations that were highly popular turned out not to be,” Jacobs says. “In some cases, stations that weren’t successful during the diary days looked better at PPM.”

Results varied by market, but generally, PPM ratings showed fragmented listening: People listened to more stations for less time. A person who wrote in their diary that they were tuned to public radio nonstop for their one-hour commute might instead be shown as listening for 12 minutes, then switching between Howard Stern, classic rock, and top 40 before switching back to NPR a half hour later. Radio programmers adapted to this, and they learned how to play to the PPMs.

“Talk got dialed back. To some degree, playing new music was seen as something of a liability,” Jacobs says. “It even had an effect on something as mundane as where stations played their commercials — the more commercial breaks you take, the lower your ratings are going to be.” That led to stations playing more commercials in fewer blocks during each hour.

“Certain formats disappeared,” says media consultant Mark Ramsay. “There was a format called smooth jazz. PPM killed it. It was doing quite nicely prior to PPM and PPM killed it.