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Politics : View from the Center and Left -- Ignore unavailable to you. Want to Upgrade?

To: Lane3 who wrote (111858)	5/26/2009 4:55:55 PM
From: TimF	Read Replies (1) \| Respond to of 541813

A response to a New York Times article talking about the percentage increase in risks of certain types of cancer from eating well done grilled meats, makes a point about use of statistics. ---- It’s just astounding how poor so much of the health and medical coverage is, even at the NYT. First of all: “barbecued and smoked meats raised breast cancer risk by 47 percent compared to those who ate the least meat.” This is an increase in the relative risk, not the absolute risk. This is meaningless as a guide to decision making without knowing the baseline level of risk. For example, a risk from 0.0004 to 0.0006 is a relative risk increase of 50%; but so is an increase from 30% to 45%. An intervention might be worthwhile to avoid an increase from 30% to 45%, but not to avoid an increase from 0.006. Always report the base rate when you report a relative risk increase or decrease — the information is simply meaningless without it. Second, are these randomized, controlled studies in which individuals were assigned at random to high-barbeque vs. low-barbeque diets? Of course not. So it’s impossible to conclude that barbequed meat “raised the risk.” As much as Times bloggers loves these sort of retrospective/observational studies, they are often deeply flawed and usually tell us little about true health risks because they are confounded by extraneous variables. In other words, there are probably many dietary and behavioral and even occupational differences between people who lots of barbequed meat and those who do not, and it’s not a simple matter to untangle the effects of all of these factors on cancer risk or any other health outcome. These kinds of retrospective studies led a lot of people to believe that hormone replacement therapies was good for, but when they did the controlled studies, they found that the benefits were outweighed by the risks. — pierce moffett well.blogs.nytimes.com