As smoking rates decline in the U.S., so does the visibility of tobacco products in primetime television.

In what they’re claiming is the largest-ever study linking tobacco use to TV, researchers at Annenberg Public Policy Center found that tobacco use on broadcast television dropped from a high of 4.96 instances per hour of programming in 1961 to 0.29 instances per hour in 2010.

The study covered 1,838 hours of popular U.S. primetime dramas from 1955 to 2010 including, “Gunsmoke,” “The Fugitive,” “Charlie’s Angels,” “Miami Vice,” “ER” and “CSI: Crime Scene Investigation.”

Cable television shows such as AMC’s “Mad Men,” where cigarettes are commonplace, were not included.

Researchers found that smoking on TV and actual smoking were linked, where the smoking decline on TV could predict the prevalence of smoking year-to-year in society.

The study found that an annual change of one tobacco instance per episode hour across two years was associated with an annual change of 38.5 cigarettes, or nearly two packs per U.S. adult.

The researchers drew their sample from Nielsen’s annual list of the top 30 primetime network dramas by watching the shows and recording  smoking, purchasing, handling and chewing tobacco products, including cigarettes, cigars, pipes, and chewing tobacco.