News ratings for the week beginning Sept. 29 were affected by a software error that created miscalculations of television viewership dating back to last March. Industry officials said the error meant ABC's viewership was consistently over-estimated.
Nielsen had said last week that ABC's "World News Tonight" had averaged 8.42 million viewers for the affected week to 8.25 million for NBC's "Nightly News." NBC hadn't lost a week since 2009.
But in its review, Nielsen found that NBC actually won the week by 170,000 viewers.