Vioxx: Excess Deaths, Excess Liability?
In the reporting about Vioxx, I've seen a lot of citations of epidemiological estimates of the excess deaths and heart attacks, which range from 35,000
. I've also seen a lot of estimates of Merck's potential liability, which are said to range from a few billion dollars up to $50 billion
. But I haven't seen any estimates of the figures you'd actually need to estimate the potential liability. It seems to me that the relevant figures are simply deaths, not "excess" deaths.
"Excess" deaths are something of a statistician's fiction. It's not like there's any clear method to distinguish someone killed by a Vioxx-induced heart attack from a Vioxx user who would have had a heart attack anyway. To see what I mean, consider the estimates of David Graham, the FDA whistleblower-scientist
Graham finds that about Vioxx users suffered heart attacks (fatal and not) at a rate of about 8 per 1000 person-years. Those using other anti-inflammatory drugs had a rate of 5 per 1000 person-years. The difference, 3 per 1000, is an estimate of excess heart attacks (it's not actually the estimate Graham uses, but it's close).
Since, Vioxx was used for about 10 million person-years, we get:
80,000 heart attacks among Vioxx users
50,000 heart attacks among similar patients using other drugs
which implies 30,000 excess heart attacks.
The final number (30,000) is what the epidemiologists focus on, and what gets reported in the newspapers. But the total number of heart attacks (80,000) is the relevant count of legitimate lawsuits. It's not like the coroner can examine the blood clot clogging somebody's arteries and look for Vioxx molecules. Although randomized trials have shown that Vioxx raises the likelihood of heart attacks, they don't tell us which particular Vioxx user died because of the drug, and which ones would have died anyway. So Merck's potential liability is awfully big (I'm shorting their stock).
From the point of view of economic efficiency, I think Merck is going to end up paying too much, even leaving aside any bogus lawsuits that are filed. Merck ought to be liable for the excess heart attacks and other diseases they caused, not the illness that would have occurred if Vioxx had never been invented. But even though only about a third of the heart attacks suffered by Vioxx users were actually caused by Vioxx, there's no way to tell which are which. So Merck will probably end up paying for all of them.
I don't see any way around this, except for dividing the court awards by three, which might not be such a bad idea.