The 2014–'15 TV season ended Wednesday, May 20, and over at Advertising Week, Jason Lynch pulls out the year-end Nielsen ratings data for the big four broadcast networks.

He zeroes in on the numbers in the 18-to-49-year-old demographic — the one advertisers most care about — and as you can see, those numbers are really, really close.

NBC: 2.4 CBS: 2.3 ABC: 2.2 Fox: 1.9

The best way to understand these numbers is, roughly, as a percentage. It's somewhat more complicated than that, but for the most part, what you're looking at is the percentage of total 18- to 49-year-olds that watched a network's programming over the past TV season. So 2.4 percent of the time, people between those ages were watching NBC between September of 2014 and May of 2015.

Compare those numbers with the year-end total viewership totals — an estimate of how many total viewers of any age, on average, watched that network — and the space between networks opens up considerably.

CBS: 11.3 million NBC: 8.6 million ABC: 8.0 million Fox: 5.8 million

You can see CBS's conundrum here. More people watch it than any other network, but fewer of those people are the younger viewers advertisers are interested in. Indeed, the show on the network with the lowest median viewer age is 2 Broke Girls, which boasts a median age of 53.

Network TV is collapsing

The real value in Lynch's post is that he compares the networks through the years, so you can see just how much the 18–49 ratings gulf has been narrowing in recent years, as more and more young viewers embrace watching on their DVRs or streaming platforms.

Look, for instance, at the final numbers for just five years ago — the 2009–'10 TV season.

Fox 3.7 CBS 3.2 ABC 2.7 NBC 2.7

And look at the 2010 and 2015 numbers side by side.

Aside from NBC and Fox swapping positions, what's most interesting here is how much space there was between the top two spots in 2010, then how much space there was between CBS and the bottom two networks. (Also of note: NBC was in last place in 2010 and still posted a better number than its first-place finish in 2015.)

The networks are basically tied

Making the effects of this shrinking audience even worse is the fact that the Nielsen ratings are based on a statistical sample. They don't actually count every viewer in the United States.

Now, Nielsen has an excellent statistical sample, by all accounts, but any time the numbers start getting so small, a change of just a couple of variables can cause enormous fluctuations, which means that small differences between networks might not actually be meaningful — but noise.

As Kyle Killen, a veteran showrunner and ratings follower, put it to me when I talked to him for a story running later: "You will see these things like a 50 percent spike in the ratings of a show, but it's almost meaningless because the numbers you're talking about are so small that them jumping 50 percent feels like noise in the data. It takes very few people to make that jump."

We don't get margins of error for Nielsen ratings. As a friend in the industry put it to me, we tend to think of the Nielsens as an election held every night, when it's really closer to a nightly poll of the viewing audience.

Obviously, nine months' worth of data averaged together is more meaningful than the instant, overnight ratings, but the numbers are still getting so small, so consistently, that very small things can affect them, as we saw when Nielsen revealed it had misreported some numbers for ABC in earlier years.

To that end, it might be more useful to think of the 18–49 numbers for the 2014–'15 season this way: the top three networks finished in what's basically a tie for first place, with Fox just barely missing out. And not one of the four came close to its numbers from just five years ago.

Correction: The original version of this article incorrectly implied that the ratings point measures the percentage of TVs tuned to a certain network. In reality, it simply measures the total possible audience within the demographic specified. The "share" measures the percentage of TVs that are tuned to a certain channel.