By Anthony Crupi
Advertising Age

While prime-time TV usage is in some ways relatively stable, with the proportion of people watching TV this season slipping just 5 percentage points from a year ago, women in advertisers’ key age groups are disappearing at a disproportionate clip

From Sept. 22 to Oct. 27, for example, the percentage of 18-to-49-year-old women watching TV in prime time fell 9 points from a year earlier, according to Nielsen stats.

The declines reached double digits on Tuesday and Wednesday; Tuesday of late has been a tough night for marketers looking to reach women, as the most female-skewing shows — “New Girl,” “The Mindy Project,” “Selfie,” “Manhattan Love Story” and “Forever” — are also the lowest-rated.

That women in the most advertiser-friendly demo are vanishing is disconcerting enough; what’s particularly unsettling is the rate at which younger female viewers are tuning out. Season-to-date, the percentage of women 18-to-34 watching TV is down 13 points, while women 18-to-24 are down 17 points. If not for the stabilizing influence of Sunday nights, when declines are in the single digits, the younger demo would be off by more than 20 percentage points.

Among younger viewers, the biggest migrations away from the tube have taken place on Monday nights. Oct. 6 was a doozy, as women 18-to-24 plummeted 30 percentage points, although the night of Oct. 26 was nearly as rough (down 26 percentage points).

Even the indomitable Shonda Rhimes is no guarantee of drawing a young, female audience on Thursday nights. While “Scandal” and “How to Get Away with Murder” ran the table on Oct. 23, they did so largely without the support of women in the 18-to-24 set, the “persons using television,” or PUT, levels for which were down 24 percentage points on the night.

It’s not just a broadcast issue. An exodus of younger viewers took its toll on some of the leading female-centric cable nets, as Lifetime saw its overall third-quarter ratings deliveries skid 24%, while Bravo dropped 22%, according to Nielsen research. Broad-reach cable channels also were vulnerable; in the same period, the top-rated USA Network lost 20% of its total prime time audience.

While older women remain faithful TV watchers, even the senior-most demographically relevant group is on the wane. Season-to-date, TV usage among women 25-54 is down 7 percentage points.

At the same time, the opposite sex is holding its ground. As much as men are considered to be elusive for advertisers, declines in the male demos are considerably less marked. PUT levels among men 18-to-49 are off 7 percentage points, while the 18-to-34 crowd is down 8%, 18-to-24-year-olds are down 11 points and men 25-to-54 are off 5 points.

TV use among men has remained fairly constant on Sunday nights, home to NBC’s top-rated prime time football showcase. CBS’s new Thursday Night Football package also seems to have helped keep guys glued to the tube. In fact, Thursday, Oct. 2, was the only night in which any of the eight key demos demonstrated year-over-year PUT growth: Usage among men 18 to 24 inched up 1 percentage point as the Packers routed the Vikings.

Researchers say they first began to detect quantifiable proof of a seismic shift in female viewing patterns back in 2013, when Nielsen (briefly) began including broadband-only homes in its ratings sample. “I think it’s safe to attribute much of the declines we’re seeing to over-the-top services,” said Brad Adgate, Horizon Media research director, referring to services that stream video over the web. “Younger people are more likely to migrate to other platforms — it’s not as if they’re watching any less content, it’s just getting more difficult to measure what they’re watching.”

Of course, if a platform isn’t rated by Nielsen, any extracurricular delivery is effectively dross. “It’s great that there are so many ways to engage the consumer, but it doesn’t do my clients much good if the deliveries aren’t being measured,” said one national TV buyer. “If young women are leaving TV faster than we can figure out where they’re headed next, how can I be sure I’m reaching them?”

As women continue to stream through the exits, those who are sticking with linear TV are getting older and older. Per MoffettNathanson Research analyst Michael Nathanson’s calculations, the median age of broadcast viewers is 54 — antediluvian by advertisers’ standards. The median age for all network and cable viewers is 44, or 7 years older than the average American citizen. Mr. Nathan attributes the greying of the tube to “lower TV penetration … in under-25 households” and the increasing use of time-shifting technologies.

As the very people for whom so much of TV is made continue to glide off the radar screen, marketers can take some small comfort in the PUT stats for certain hours. While the five-week sample size is admittedly limited, the early numbers suggest that younger women are more likely to watch live TV in the 9-10 p.m. hour. Given their skew and time slots, you could do worse for your client than buy time in shows like “Scandal,” “The Good Wife” and “Jane the Virgin.”