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Monday, July 14, 2014

Alcohol Deaths

A recent CDC study that claims alcohol consumption is killing "1 in 10 adults" and is the "leading cause of preventable death" based on 88,000 deaths in working age adults (20 to 64) between 2006 and 2010. These deaths were "due to health effects from drinking too much over time, such as breast cancer, liver disease, and heart disease, and health effects from consuming a large amount of alcohol in a short period of time, such as violence, alcohol poisoning, and motor vehicle crashes".

I don't think anyone is surprised that "drinking too much" is bad for you. However, before we revisit prohibition, maybe we should look at the CDC study more carefully.

The numbers are based on data for "Alcohol-Related Disease Impact (ARDI)" data provided by nation-wide and state counts of alcohol-attributable deaths.  This concept has been around since at least the early 1990s.  Look at the list of causes in the quote. Breast cancer?  Heart disease? Are they really claiming that breast cancer is caused by booze?

Not exactly. The second link doesn't have all the details but it explains that they try to separate deaths completely caused by alcohol from those sometimes caused by alcohol and adjust the data accordingly. There's something called an "alcohol-attributable fraction (AAF)". For example, they take the total number of breast cancer deaths and multiply by the AAF to estimate the number of alcohol-attributable breast cancer deaths. The concept isn't necessarily bad, but like all statistics, the AAFs are estimates and aren't estimated the same way for each cause of death. In other words the 88,000 number is an estimate based on estimates of estimates but they don't provide a margin of error on their estimate.

That doesn't mean that the basic claim is wrong.  Excessive alcohol consumption is a serious problem. However, instead of aggregating a bunch of estimates into one big scary number that isn't necessarily accurate, I'd prefer a table showing what alcohol does. Put the cause of death in Column A and an explanation in Column B. Put "Breast cancer" in A and in B explain how excessive alcohol consumption increases the risk of incurring breast cancer and dying from breast cancer. Do the same with "Heart disease", "Liver disease", etc.

Why don't they do that? I can think of two possibilities:
1) They think most of us are too stupid to understand a table. Sadly, they could be right.
2) Many of these causes of death have small AAFs (in other words, few alcohol-related deaths) so they wouldn't be impressive listed individually. However, added up, they help make the one, big scary number even bigger.

Note: The first link, the most recent study, says that alcohol is the "leading cause of preventable death." The second link is 10 years older and alcohol was merely the "third leading preventable cause of death". Does that mean that alcohol deaths increased relative to population size or other deaths decreased? Maybe someday I'll chase the data and find out.

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