According to Radiolab, about 12 million people were listening when Welles’ broadcast came on the air and “about 1 in every 12 … thought it was true and … some percentage of that 1 million people ran out of their homes.”

“That constitutes a major freakout,” Radiolab says.

Well, Slate has a different opinion. “The supposed panic was so tiny as to be practically immeasurable on the night of the broadcast,” it concludes. According to Slate:

“Far fewer people heard the broadcast — and fewer still panicked — than most people believe today. How do we know? The night the program aired, the C.E. Hooper ratings service telephoned 5,000 households for its national ratings survey. ‘To what program are you listening?’ the service asked respondents. Only 2 percent answered a radio ‘play’ or ‘the Orson Welles program,’ or something similar indicating CBS. None said a ‘news broadcast,’ according to a summary published in Broadcasting. In other words, 98 percent of those surveyed were listening to something else, or nothing at all, on Oct. 30, 1938. This miniscule rating is not surprising. Welles’ program was scheduled against one of the most popular national programs at the time — ventriloquist Edgar Bergen’s Chase and Sanborn Hour, a comedy-variety show.”

Slate also argues that there’s no data to support the idea that many radio listeners heard about the broadcast and tuned in during it. And it points out that “several important CBS affiliates (including Boston’s WEEI) pre-empted Welles’ broadcast in favor of local commercial programming, further shrinking its audience.”

So how did the story of the “panic” grow over the years? Slate blames newspapers, which allegedly “seized the opportunity presented by Welles’ program to discredit radio as a source of news. The newspaper industry sensationalized the panic to prove to advertisers, and regulators, that radio management was irresponsible and not to be trusted.”