If you’re a reality competition series that’s been on the air as long as “American Idol,” “Survivor,” or “The Amazing Race,” it’s never easy to know if it’s time for a change to your proven format, or if you should stick with what your audience knows and loves.

It’s a dilemma that can rattle producers. How they tackle this problem can make or break a show that’s built a loyal following but still needs to remain relevant.

“This question of whether to stick with what you know is working or make certain changes goes to the heart of both reality and scripted television,” says Jane Tranter, exec VP and head of BBC Worldwide Prods. “The truth is that you’re never completely sure, but I think you want to maintain that connection with what people like, while at the same time, we can’t just do the exact same thing with ‘Dancing With the Stars’ that we’ve always done.”

For Tranter, casting is a fundamental way to keep things alive on “Dancing With the Stars.” Kirstie Alley, who might not seem like an obvious choice for the show, became a season favorite most recently, though she placed second in the finale.

“Top Chef” executive producer Dave Serwatka agrees that finding the right mix of contestants is one of the most successful elixirs in reality television. And it requires time and research.

“We have our ear to the ground to find up-and-coming young chefs, and we try to find people who have that thing that makes you want to watch them no matter what they’re doing,” says Serwatka. “You can change the show a lot, but the people have to be interesting.”

Jeff Probst, host and producer of “Survivor,” also believes casting is the best way to keep a show compelling to viewers so they return season after season.

“People want the same thing, but they want it given to them in a slightly different way,” says Probst. “We may go from location to location, but we’re always showing you people struggling to win a competition under tough circumstances.”

Some shows alter their format or structure in much bigger ways. The changes don’t always go over as hoped but, when cast changes happen as they did on “American Idol,” the show still must go on in one form or another.

“I watched them put four judges in, I watched them bring the safeguard in, mix the chemistry of the judging up, focus on the judges rather than the contestants, and I thought, ‘These are mistakes being made in front of my very eyes,’?” says Nigel Lythgoe, who was a producer on “American Idol” for seasons one through seven, then left the show during seasons eight and nine and returned for the current season. “I wonder if I’d have done the same thing if I had been there.”

Longtime reality show producer Jonathan Murray has spent decades struggling with the same problem, most recently on “Project Runway.”

“When we were first asked to work on ‘Project Runway’ we realized we just had to not screw it up,” laughs executive producer Murray, who started on the show when it moved from Bravo to Lifetime. “But we had great material so it made sense to expand to 90-minute episodes.”

Other shows are simply set up to include constant change as part of their design. So the burden falls to the producers to continually redesign the structure of the competition.

“I think the way our show is set up, that provides a lot of the sense of newness for the audience,” says “Amazing Race” executive producer and director Bertram Van Munster. “We’re constantly in different countries with a different cast on a different challenge, so no two shows are alike.”

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