Surgeon General Vivek Murthy’s recent advisory that drinking alcohol raises the risk of cancer is something of a gamble. It’s a bet that telling people to do less of something they enjoy will be taken in good faith, and not as a politically motivated judgment of their lifestyle choices. It also exemplifies some perennial challenges in public health. Communicating about risk in an intelligible, actionable way to the public is hard to do without oversimplifying things. Helping policymakers and people decide what to do with the information is even harder.

The advisory relies on decades of epidemiologic studies and experiments testing what happens to mice who are given alcohol. (The poor, drunk mice develop tumors.) It’s a synthesis of information gathered across time, nations and many hundreds of thousands of people.

Even though the advisory relies on mostly observational studies and not randomized controlled trials, the relationship between alcohol and cancer has been demonstrated consistently enough that we can have confidence that it’s reliable; it’s a recurring signal heard through so much noise. The medical community also has theories about how alcohol causes cancer, through DNA damage and inflammation. The case is strong. But in terms of how usefully and precisely the advisory elucidates cancer risk for various levels of drinking, I’m less sure.

The report describes the relationship between alcohol and cancer in different ways: the number of new cases of cancer a year in the United States potentially related to alcohol consumption (roughly 100,000); the number of annual cancer deaths that might be attributed to alcohol (roughly 20,000, compared to nearly 200,000 cancer deaths attributable to smoking); the increase in absolute risk for developing alcohol-related cancers (a 2.5-percentage-point increase for women and a 1.5-percentage-point increase for men); and the relative risk for specific cancers, such as breast cancer (one study suggests that a drink a day increases a woman’s risk by 10 percent).

But it’s hard for individuals to translate statistics to their own lives. A small increase in relative risk is difficult to make meaningful, even for people who understand what “relative risk” means. (It doesn’t mean a 10 percent risk of breast cancer; it means women who drink may be 10 percent more likely to get breast cancer than women who don’t.)

Among national universities, Princeton was ranked No. 1 again, followed by the Massachusetts Institute of Technology and Harvard. Stanford, which tied for third last year, fell to No. 4. U.S. News again judged Williams College the best among national liberal arts colleges. Spelman College was declared the country’s top historically Black institution.

There are many other open questions that might seem important to a person deciding whether to change her habits: Is a glass of wine as carcinogenic as a daily martini? Does it matter how old you are when you start or stop drinking? And perhaps most important, do you lower your cancer risk if you quit drinking tomorrow, regardless of your age? The answers to all of these questions are unclear.

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