Researchers believe a drop in the U.S. smoking rate could be thanks to a "dwindling" visibility of cigarettes on primetime TV.

The smoking rate has decreased by two cigarette packs a year per adult, a BMJ-British Medical Journal news release reported.

The research team watched and coded 1, 838 hours of popular "U.S. prime-time dramas broadcast" that aired between 1955 and 2011 to see how the portrayal of tobacco products affected smoking rates.

The researchers found that "smoking, purchasing, and handling" of tobacco has fallen dramatically since the 1950s. The team observed that tobacco use on TV fell from 4.96 instances per hour of programming in 1961 to 0.29 instances per hour in 2010.

"After taking account of changes in cigarette prices and other influential factors, the authors calculated that one less tobacco event per episode hour across two years of programming significantly predicted an annual fall of nearly two packs of cigarettes (38.5 cigarettes) for every US adult," the news release reported.

The price of tobacco is also believed to affect smoking rates. The researchers compared these effects with those related to tobacco use on Television.  The team found tobacco use on TV had a significant effect on smoking rates in viewers.

"But importantly, the findings also suggested that continuing TV depiction of tobacco use may have hindered an even faster decline of the leading cause of preventable death in the United States," the news release reported.

The finding backs up past research that shows exposure to tobacco in the media can prompt cravings in those viewing the program.

"The depiction of smoking in other screen media, such as cable TV and YouTube, should be studied further in the United States and internationally in countries with high rates of smoking and TV use, they conclude," the news release reported.