The study didn't prove cause-and-effect between letter grades and food poisonings, but one of the researchers, UCLA economist Phillip Leslie, said the decline is unlikely to be a coincidence.

"You really have to twist yourself into knots to believe that," he said.

Restaurant revenues also changed after grade cards were posted, the group found in another study. Restaurants with "A" grades saw an average 5.7% increase in revenues and those with "B" grades gained 0.7%. In restaurants with "C" grades, revenues dropped by an average of 1%.

On the downside, the group also concluded that implementing grade cards made inspectors slightly more lenient and led to grade inflation at the cutoff points between an "A" and a "B," or a "B" and a "C." In other words, inspectors were rounding up grades when it was close.

That doesn't surprise Kansas State's Powell, who helped design a restaurant inspection system for New Zealand and was not associated with the Los Angeles studies.

"Restaurant owners tell us that 'We need an "A" on that door and I will do whatever is necessary to get that "A" '," he said.

Fresno County's Robinson raised the possibility that restaurant owners might also pressure inspectors for a favorable grade -- even offer them bribes -- if the results were posted in their windows. He said that was another reason for the county's past reluctance to post inspection results in restaurants.

"We don't want to put our staff in that situation, where there's any kind of manipulation, or indignation or anything like that to get a particular grade," he said.

Leslie is unconvinced by the suggestion that there might be bribery.

"To my knowledge there's no real evidence of this happening where grade cards have been implemented," he said. "It seems to me that it's a poor reason not to implement grade cards."

Chamorro of the California Restaurant Association said her group's view on posting grades is starting to evolve. Though her members are still happy with Fresno County's current system, she said they are also open to change.

"We don't outright oppose a letter grading system," she said.

Lorraine Salazar, co-owner of the Sal's chain of Mexican restaurants, echoed Robinson's objection that posting grades could give the public a false sense of security. Still, she might support it if the same system was in place everywhere.

"If we're going that route, I'd like to see something happen at the state level," she said. "I'm not opposed to it but certainly it needs to be consistent."

Advocates of posting inspection results in restaurants say the benefits are twofold.

First, it gives information to consumers in a format that is easy to understand and available exactly when they need it -- when they're picking a place to eat.

Second, it helps create what Powell calls a "food safety culture" in which restaurant managers and employees are routinely watching for unsafe conditions nd correcting them, regardless of whether an inspector is present.

"This is just a basic check to hold people responsible," Powell said. "This is just one little tool."

Leslie describes posting restaurant inspection results as an example of using information disclosure as a tool to achieve public policy goals.

It's similar, he says, to publicizing school test scores as a way of improving education, or hospital complication rates as a way to enhance health care quality.

"Putting a letter grade in the window is such an ideal way of doing this," Leslie said. "People know what it means ... and you see it before you go into the restaurant. This is a really compelling, specific example of how notifications should work."