Underscoring how potent cable programming has become, AMC’s zombie series “The Walking Dead” completed its fall season Sunday night with higher ratings in the most important audience category for advertisers — viewers between the ages of 18 and 49 — than any show on the broadcast networks.

Over all, “Walking Dead” averaged a 5.3 rating in that 18 to 49 age group, for its first airing of each episode, a number that topped the initial rating for that category for such network hits as “The Big Bang Theory,” “Modern Family” and “The Voice.”

The show’s finale Sunday night averaged 10.5 million viewers, just short of the record that the show set for cable television with its premiere this season, 10.9 million viewers. Either total would rank as a hit number by any television standard.

But “Walking Dead” has proved to be especially valuable for his appeal to younger viewers. Sunday’s finale was seen by 6.9 million viewers in that 18 to 49 segment of the audience. By comparison, the top network series “Big Bang” has averaged 6.3 million for its first day of exposure.