Keep an eye on unemployment if you want to know how theme parks are going to perform. Nicholas Colas at ConvergEx has apparently examined 30 years worth of visits to national parks and visits to theme parks, and discovered that they’re inversely correlated. The primary factor appears to be unemployment, because visits to national parks are much less expensive than, say, visiting Mickey at Walt Disney‘s (NYSE:DIS) theme parks.

Having done both, here’s what I can report. I’ve visited a fair amount of parks in my time: Yosemite, Sequoia, Rocky Mountain, Bryce, Zion, Capitol Reef, Arches, Glacier and Banff to name a few. If you’ve never experienced the grandeur they offer, you’re missing out. I’ll trade a few days of the most jaw-dropping natural beauty and peace for a two-minute ride on Space Mountain any day.

I’ll also save myself scads of money. National parks costs include the plane fare, a rental car, a hotel and nominal entrance fees. The parks are located in rural areas, and so they’re often lacking in 4- and 5-star hotels. Thus, you’re looking instead at mid-market and limited-service chain hotels, B&Bs or family-owned motels that simply aren’t that expensive.

The same goes for restaurants. You’ll often find family-owned restaurants that have been around for years that serve delicious local fare for a reasonable price. Entrance fees are usually per car, and not per person. You bag your lunch while you hike or drive around the park and visit general stores for food and snacks. Souvenirs are usually low-priced tchotchkes that are nice little reminders of your visit.

Contrast this to visiting Disney, or the amusement parks of Cedar Fair (NYSE:FUN) or Six Flags

(NYSE:SIX). You might also have to fork over plane and rental-car fare, so that may not be too different. Some hotels might be priced the same, but if you want to stay anywhere near the resort, you’re likely looking at hundreds per night. And the kids may want room service.

When you go to the park itself, you have to pay for parking. Then comes the entrance fee, which is per person. Inside the park, food prices are marked up big-time since you’re a captive audience, and it isn’t usually very good food. Every time you exit a ride like Star Tours or Space Mountain, you end up walking through a gift shop of expensive merchandise.

Get the picture, Pluto?

So it stands to reason that as unemployment squeezes the nation’s pocketbooks, national parks start to seem like a pretty good deal. And with the ever-increasing obesity epidemic, parents may want to get themselves and their children more healthy by moving around in the great outdoors.

So keep an eye on attendance at the theme parks, which are reported monthly or quarterly. If you see it start to drop-off along with a rise in the unemployment rate or labor force participation rate, and especially if national park attendance rises, consider buying puts or shorting (except Disney, which is too diversified for theme park visits to have a giant impact). Also consider the same for the lower-end hotels, such as those held by Wyndham Worldwide (NYSE:WYN).

Lawrence Meyers does not hold a position in any stocks mentioned.