CBS and Fox split ratings honors last week, with CBS leading among total adults and Fox among viewers 18-49. But ABC also claimed boasting rights as its Monday-night edition of Dancing With The Stars turned out to be The The highest-rated show of the week. In a ratings anomaly, however, it was not the most-watched show -- that honor went to Wednesday night's American Idol , which drew 23.95 million viewers versus 22.66 million for Monday's Dancing. The explanation for the apparent discrepancy is that ratings are based on the percentage of total viewers tuning in -- and there were more viewers watching TV on Wednesday than there were on Monday, thereby allowing Dancing to post higher ratings with fewer viewers. Among the nightly newscasts, NBC Nightly News with Brian Williams averaged 9.17 million viewers (more viewers than for any NBC primetime program last week). ABC World News with Diane Sawyer placed second with 8.34 million. The CBS Evening News , which was preempted by CBS basketball coverage on Thursday and Friday, averaged 5.97 million viewers on the other three days. (TVNewser observed that Evening News saw its lowest ratings for the first quarter since Nielsen began tracking the CBS newscast in 1992.) Overall, CBS finished the week with an average 6.2 rating and an 11 share. Fox came in second with a 5.2/9. ABC finished third with a 4.9/8, while NBC finished last with a 3.7/6.