After a strong debut week, O'Brien's total audience fell precipitously over the summer months, and the program began losing to "Late Show with David Letterman" in overall ratings. In contrast, O'Brien's performance in the crucial 18–49 demographic was favorable, and it was found that he had brought down the median age of "The Tonight Show" audience by a decade compared with his predecessor, indicating that a generational shift was taking effect as O'Brien established himself in an earlier timeslot. Taking this into account, columnist Tom Shales assessed in August 2009 that O’Brien was in a better position than Leno had been when he began his "Tonight Show" run in 1992; Leno consistently lost to Letterman in the ratings for eighteen months before eventually cementing his number one status.