In 2010, New York City health officials launched a new food safety tactic that assigned restaurants an inspection-based letter grade and required that the grade be posted where passersby could easily see it. So, did this grading make a difference? A new study finds that it has, with the probability of restaurants scoring in the A-range up by 35 percent.

To conduct the study, researchers with the New York City Department of Health and Mental Hygiene examined data from more than 43,400 restaurants inspected between 2007 and 2013. A restaurant’s score is based on how well it complies with local and state food safety requirements, such as food handling, food temperature, personal hygiene and pest control. Each violation is assigned a set of points, which when tallied up result in a letter grade of either A, B or C. The lower the score, the better the grade. (Click here for more on how the grades are tallied.)

The study, which was published in the March issue of the American Journal of Public Health, found that the proportion of restaurants with A-range scores rose from 28 percent in July 2008 to 31 percent in July 2010 to 46 percent in July 2013. In addition, the median initial inspection score went from 21 points in July 2008 to 17 points in July 2013 (remember, a lower score is better).

Regarding specific food safety regulations, researchers found that when compared to the two years before grading began, many restaurants were in better compliance. For example, the study found that average points given to all restaurants substantially declined for evidence of pests, such as rats, mice or roaches as well as for inadequate hand-washing facilities and not having a food safety-certified supervisor on site. Overall, fewer inspection points were also given for improper storage and inadequate food worker hygiene. However, average points went up for improperly maintaining food contact surfaces and increased slightly for inadequate protections against food contamination. Still, the proportion of C-range restaurants declined from 29 percent in July 2008 to 22 percent in July 2013.

In addition, the study found that more restaurants acted to correct cited violations — in July 2013, 45 percent of restaurants requiring reinspection received an A grade, up from 34 percent in July 2011. Study authors Melissa Wong, Wendy McKelvey, Kazuhiko Ito, Corinne Schiff, J. Bryan Jacobson and Daniel Kass write:

The NYC Health Department launched the restaurant letter-grading program to motivate restaurants to improve food safety, inform the public about inspection results, and reduce illness associated with dining out. …Our restaurant hygiene analysis suggests that the program provided an effective incentive for operators to comply with regulations and improve practices. We also found that there is an incentive to maintain hygiene practices, with the majority of A-grade restaurants earning A grades on their next inspection cycle.

The researchers also assessed public perceptions about the letter-grading program, using results from two independent telephone surveys. They found that more than 91 percent of New Yorkers approved of the program and 88 percent considered the inspection grades when deciding where to dine in 2012.

According to recent data from the Centers for Disease Control and Prevention, more than 1,600 foodborne disease outbreaks occurred in 2011-2012, including more than 29,000 illnesses and 1,750 hospitalizations. Restaurants were the most common source of outbreaks traced back to a single known food preparation setting.

To learn more about the letter-grading study, visit the American Journal of Public Health.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.