The change in the September ratings was most noticeable at 8 p.m., where CNN has moved its best-known host, Anderson Cooper. The network’s performance during that hour has improved by 38 percent over last year, growing to 215,000 viewers from 156,000.
On MSNBC, meanwhile, Lawrence O’Donnell has lost 100,000 viewers from the numbers Mr. Olbermann posted last September, with 185,000 viewers in the 25-to-54 age group, a drop of 35 percent. (Bill O’Reilly on Fox, as always, dwarfs his competitors with about three times as many viewers, 611,000.)
More ominously, the falloff for Mr. O’Donnell seems to be affecting MSNBC’s biggest name, Rachel Maddow. Her audience dropped 15 percent this year, to 245,000 from 289,000. She still beats Piers Morgan on CNN in the 9 p.m. hour, but his show has improved 18 percent over Larry King’s ratings last year, with 193,000 viewers to Mr. King’s 164,000.