A new study from Jacobs Media asked over 25,000 respondents from over 75 Rock-formatted stations about their response to Howard Stern's jump to Sirius. The results show that Stern’s move has indeed helped the satcaster match or surpass the subscriber rate of XM among Rock fans. However, roughly 70 percent of Stern’s regular listeners say they have not followed him, and stuck with commercial radio morning shows.

The study shows that the popularity of Sirius and XM is basically dead-even (both with six percent). Of those who say they are likely to subscribe this year, Sirius ranks ahead of XM.

Unsurprisingly, Stern is the key factor in Sirius subscriptions, cited by one-third of respondents. However, the study also shows that Stern fans who planned on switching to Sirius may have already all done so. Most of his fans surveyed who were following him to Sirius have already signed up, with a smaller percentage saying they will buy Sirius later in the year.

Looking just at markets where Stern was on-air in 2005, one-fifth of those surveyed who considered themselves "regular listeners" to his show have already subscribed to Sirius, with one in ten indicating they plan to do so. According to Jacobs' study, this is a "strong indicator that for commercial radio broadcasters in [former] Stern markets, the worst is over."

However, the majority of Stern's former "regular listeners" have just stayed with terrestrial radio morning shows in their market, so once the ratings come out, many morning shows should expected growth in their audience bases in Stern's absence.

On average, defections to Sirius were no greater among listeners to former Stern stations. However, some former Stern stations were able to retain a much higher percentage of his audience for his replacements, but in other cases, defections were quite higher than average.

In this chart above, one-fifth of former Stern listeners bought Sirius, with almost one in ten planning to.

In the chart below, for example, Station 1 has kept over half of Stern’s listenership, while other stations have not.

The biggest winners in the study are many of Stern’s former competing stations. Five of these stations from markets  were specifically isolated to analyze the benefits of losing Stern as competition for their morning shows.

As seen above, 46 percent of regular Stern listeners have stayed with the station’s new morning show. Three of Stern's former competitors saw their morning shows attract almost six of every ten of his ex-listeners. According to Jacobs, this could indicate that the upcoming round of Arbitron ratings will show some very impressive growth among morning shows in recent months.