Consumer spending drives most of the growth in the American economy.  And that spending depends on having enough people with enough disposable income that they’re willing and able to spend. It’s a group of people we like to call the Middle Class.  Chances are you consider yourself one of them.  But how do we decide who qualifies as middle class, and how much stuff it takes to be part of it?

Those questions have no straight answers.  But a good place to find a sort of collective image of what the middle class looks like and how that image has changed over the years is Hollywood.

Once upon a time, in the 1950s, when America was still working out just what the middle class was, you could see the question getting hashed out on screen.  Up until then, we talked more about two different ends of what we now call the middle class: wage earners  on the one hand and salary men on the other.  Each group was portrayed in Hollywood.

When Ernest Borgnine won his Oscar for “Marty,” he was playing a classic wage-earner — a butcher.

On the salary man side, Gregory Peck embodied the archetype when he played Tom Rath in “The Man in the Gray Flannel Suit.”

By the end of the ’50s, it was clear that the optimism Betsy Rath expressed in that clip was well-founded. The economy was booming.  Upward mobility seemed really possible.  So much so that the worlds of salary man and wage earner began to merge.

In July of 1959, there was a sort of official declaration of this fact by the United States government, when the Department of Labor released a report titled “How American Buying Habits Change.”

“Today the wage earner’s way of life is well nigh indistinguishable from that of his salaried co-citizens,” the report announced.  “Their homes, their cars, their baby sitters, the  style of the clothes their wives and children wear, the food they eat, the bank or lending institution where they establish credit, their days off, the education of their children, their church — all of these are alike and are becoming more nearly identical.”

Or, as Kathleen Newman, a professor at Carnegie Mellon University who studies mass media and society, paraphrases: “Guess what, we did it, everyone’s middle class.  We can relax now.”

And Hollywood began to reflect that storyline back to us.  We stopped seeing many Marty the Butchers.  We got lots of men in suits, from Ward Cleaver in “Leave it to Beaver” all the way through Dr. Huxtable in “The Cosby Show” (who may have been famous for his colorful sweaters, but whose job as a doctor and  well-appointed home put him squarely in the white-collar middle class.)

For a while at least, Hollywood’s airbrushed version of the middle class made some sense. Wages for average workers were rising. A blue collar job could afford you a lot of the stuff a white collar family had. But by the late 1970s that trend was in reverse. Since then, the gap between the two ends of the middle class has only continued to widen. And Hollywood has been less quick to chart that new direction.

This disconnect was made painfully clear to a set decorator named Rosemary Brandenburg several years ago, when she was working on the set for “Castaway.” Before Tom Hanks gets in that plane crash and has to survive on a desert island, there’s a scene at his girlfriend’s parents house, eating Christmas dinner.

“We were asked to make a ‘typical middle class’ dining room/ living room,” Brandenburg remembers. “And I was too shy to  go to our director and ask him which middle class he really wanted.”

That’s when Brandenburg made her mistake.

“I made middle class in my life, which was old fashioned granny lamp shade, print couches and a La-Z-Boy chair, printed wall paper.” In short, a working class version of a “typical middle class home” — well loved, a little bit shabby.

When Rosemary had the set ready, the director came to see. “He walked in and just hated it. Said ‘What have you done here?  I mean this looks like grandma’s house!’ He had in mind someone with much more upscale tastes, and up-to-date furnishings.

Brandenburg complied with the director’s version of the middle class. She redid the set, lampshade to wallpaper. Here’s a clip — it’s a little dark, but if you look closely you’ll notice the fancier props.

After the “Castaway” experience, Brandenburg says she never worked for that director again. But she says she also learned an important lesson. “One can’t assume that middle class is middle class,” she says. Especially in Hollywood.

Hollywood’s inflated version of the middle class is still alive and well. Think about the TV show “New Girl,” where a bunch of 20-somethings on teacher, bartender, research assistant and “junior lead marketing associate” salaries, live in a gorgeous loft in L.A.

Then there’s that movie from a couple years ago, “It’s Complicated,” where Meryl Streep plays a baker who somehow lives in a House Beautiful-worthy home — literally, it was featured in the magazine — in Santa Barbara, where the kitchen alone looks like it cost a fortune. Oh yeah, and the plot of the movie centers around a remodel of said kitchen, so Streep’s character can finally get a “real” one.

Of course there’s nothing wrong with dreaming.  And Hollywood never pretended to be anything but pretend.  But consider this observation, from Damon Silvers, a labor lawyer for the AFL-CIO. When he watches this stuff, he thinks about how it shapes the collective image we have of ourselves.

“There is a tendency to imagine that we live in a country where the typical family makes $150,000 a year. But half of all American households have incomes less than $55,000 a year,” he says. “So there’s a kind of a cognitive problem here. We don’t live in the country we think we live in. The world that is projected as middle class in the media is a world that no more than something like 15 percent of America can afford.”

And yet, a lot of us try to afford it. Often by getting in lots of debt.

Listen to Krissy’s interview with Marketplace Money