"Trends observed in the machine testing data may be due, in whole or in part, to the natural variability of tobacco crops from year to year, small errors in the machine-test method and/or changes in the range of brand styles available for smokers."
Researchers, however, say that the findings point to a deliberate effort by tobacco companies.
"Our research, based on industry-provided data, showed that this increasing trend is not random," Alpert says.
"This trend is real. It is increasing, and it is not attributable to chance."
Experts not affiliated with the study agree.
"The levels of nicotine in cigarette smoke are not an accident," says Stanton Glantz, professor of medicine at University of California at San Francisco. "Cigarettes are a heavily engineered product with a number of product controls. So, if there's an increase, it was not an accident."
"The tobacco companies do knowingly and purposely control nicotine levels in their cigarettes," says Michael Cummings of the division of cancer prevention and population sciences at Roswell Park Cancer Institute in Buffalo, N.Y.
"While one might expect slight year-to-year variations in nicotine levels, the consistent upward levels found seem to suggest this is purposeful. "
The idea that cigarette companies may be deliberately increasing nicotine levels in their products may serve as grounds for litigation and governmental regulation.
"The study emphasizes the need for FDA regulation of the cigarette industry and for current smokers to seek medical help of quitting this addiction," says Erika Schlachter, director of national advocacy for the American Lung Association.
"I think this kind of information could really stimulate or jump-start congressional efforts to give the Food and Drug Administration firm regulatory authority over tobacco products," says Peter Jacobson, director for the Center of Law, Ethics and Health at the University of Michigan School of Public Health.
"If this does not stimulate regulatory action or momentum for congressional action on providing FDA oversight of this industry, it's not clear what will," Jacobson says. "This is the exact reason and rationale for why you would regulate the product market."
Connolly agrees. "It's about time that we started making national policy decisions based on science and not solely on economic interests."
Jacobson, who believes "the chances are high" that litigation will also result from these findings, says the tobacco companies may be faced with an uphill battle when it comes to defending the increase in nicotine content in their products.
"It seems to me that this kind of action will potentially lead to product liability litigation or some type of class action deceptive marketing claim," he says. "The industry will have a difficult time explaining to a jury why it was OK to add additional nicotine after saying to the public how concerned it was with public health.
"There are some real inconsistencies here, the kind which often lead to large punitive awards."
Chicago smoker Roberts says that while he is hooked on cigarettes, he does not believe nicotine is the culprit behind his addiction.