Another set of grim headlines warned that marijuana is as addictive as tobacco -- again, a conclusion that went beyond the study's findings and which was almost certainly wrong.

In this U.S. study, researchers took 12 people who regularly smoked both marijuana and cigarettes and had them stop using one, the other and both, in varying orders. Physiological tests and responses to questionnaires were used to assess withdrawal symptoms such as irritability and difficulty sleeping. The withdrawal symptoms reported were roughly comparable.

But the limitations of this research are obvious. In fairness, most were acknowledged in the study, published in the journal Drug and Alcohol Dependence.

For one, the study looked only at regular users of both substances, so it tells nothing about marijuana users who do not use tobacco -- a considerable number, by most accounts. Second, the researchers did not publish the results for individual participants. In a sample of 12, one or two extreme responses can skew the averages enough to make them meaningless.

The researchers also did not note any changes in participants' use of caffeine or alcohol, which could easily have affected their findings. Volunteers were asked not to change their use of these substances, but we have no clue whether they followed these instructions.

And though the overall withdrawal symptom ratings were similar, ratings of anger and craving were higher for tobacco than for marijuana. And even in areas where the two substances were statistically comparable, there was often a trend toward the tobacco withdrawals being stronger. Had this been a larger study, those trends might have reached statistical significance.

Also, the five-day abstinence period may not have been enough to fully gauge withdrawal effects. For longtime cigarette smokers, tobacco cravings can continue for years.

Finally, a reality check: It is an established fact that about 32 percent of those who ever touch a cigarette become dependent on tobacco. For marijuana, the figure is nine percent. In the real world, it's clear that marijuana is nowhere near as addictive as tobacco -- but again, you'd never know it from the coverage of this study.

In fact, you wouldn't learn much from the coverage of any of these studies.