Nielsen Media Research has conceded making an error and is performing a recount after the company's ratings on Tuesday initially indicated that ABC's "World News" most likely had its smallest audience ever.

The dispute with Nielsen was a downer for the network after the entertainment division -- keyed by the National Basketball Association finals -- won in the prime-time ratings for the first week since September. It was ABC's most-watched week in the summer in five years, according to Nielsen.

ABC asked Nielsen for an investigation after its ratings showed "World News" averaged 6.2 million viewers last week (4.3 rating, 9 share), its worst showing since at least 1987, when Nielsen's "People Meters" technology was introduced, and probably for many years before that. The previous week, the "CBS Evening News" hit a similar low point. ABC's average did not include Tuesday and Thursday's newscast, because "World News" was pre-empted in the West those nights for the NBA finals.

The network questioned the Friday night ratings, when Nielsen said "World News" was watched by 4.1 million people, well below its Friday average of 7.3 million this year. Friday marked TV's digital transition, when analog signals were cut off and an estimated 2.5 percent of the nation's TV homes lost their TV transmissions.

News ratings are typically down in the summer, but not by that much, ABC said. Given the relatively small number of homes losing signals, ABC claimed that a loss of more than 3 million off its season average was illogical. CBS, for example, had 5.1 million viewers Friday compared to its season average of 5.8 million that night, Nielsen said.

"The numbers don't make any sense," said Jon Banner, executive producer of "World News."

Nielsen indicated that some of the ABC affiliates that had made the digital switch early were inadvertently left out of the news ratings. The company plans to issue new ratings on Wednesday, said Gary Holmes, a Nielsen spokesman. It's not yet clear how much the error will affect ABC's ratings.

For the week, the network averages were: ABC 7.3 million viewers (4.4 rating, 8 share), CBS 6.9 million (4.6, 8), Fox 5.1 million and NBC 5 million (both 3.2, 6), My Network TV had 1.5 million (0.9, 2), the CW 1.2 million (0.8, 1) and ION Television 670,000 (0.5, 1).

ASSOCIATED PRESS

1 NBA Finals: L.A. Lakers vs. Orlando, Game 4, (ABC)

2 NBA Finals Game 3, (ABC)

3 NBA Finals Game 5, (ABC)

4 NBA Trophy Presentation (ABC)

5 The Mentalist (Tuesday) (CBS)

6 NCIS (CBS)

7 Two and a Half Men (CBS)

8 The Mentalist (Thursday) (CBS)

9 48 Hours Mystery (Tuesday) (CBS)

10 CSI: Crime Scene Investigation (CBS)

11 So You Think You Can Dance (Wednesday), Fox

12 So You Think You Can Dance (Thursday) Fox

13 Wipeout (ABC)

14 Criminal Minds (CBS)

15 CSI: Miami (CBS)

16 CSI: NY (CBS)

17 NHL Stanley Cup Final: Pittsburgh vs. Detroit, Game 7, (NBC)

18 The Big Bang Theory (CBS)

19 60 Minutes (CBS)

20 The Bachelorette (ABC)