Risk is in the Mind of the Taker
Are the premises of the guidelines flawed leading to flawed extrapolations, or are the premises correct and we just don't like the implications? Let's look at the premises - because if they're flawed, we may find that other premises we have accepted are flawed.
One basic premise of the new guidelines is that the net benefit of statins is great enough to justify their use in people with a ten-year risk of cardiovascular outcomes of 7.5%. This is based on a relative risk reduction (RRR) of these outcomes of about 27% with statins. But as readers of this blog know, relative risks are only useful to compare the relative value of treatments for the same condition in the same risk group and they tell us nothing about the absolute value of those treatments or their values compared to treatments for conditions with different base rates. A person considering taking a statin to prevent a cardiovascular event is concerned about absolute reductions in that outcome from his/her baseline level of risk. We can roughly estimate the absolute risk reduction (ARR) conferred by statins as:
(10-year risk [assuming it's linear]/10) * (1- RRR) - (10-year risk/10)
= 0.75 * (1-.27) - 0.75 = -.2025
So, given these assumptions, if your annual risk of cardiovascular badness is 0.75%, it should decrease by 0.20% to 0.55% with statins. Sounds like peanuts, right? If it does, that's because we're not accustomed to thinking about things in terms of absolute risk. Here are some events and associated risk reduction measures for comparison (click here for a better image of the table):
|House Fire deaths||0.000014||Home Smoke Alarm||0.74||0.000010|
|Motor vehicle deaths (Per Licensed Driver)||0.000180||Seat Belts||0.72||0.000129|
|Cervical Cancer Deaths||0.000024||PAP smears||0.60||0.000014|
|Colon Cancer Deaths||0.000164||Colonoscopy||???|
|Bicycle Deaths||0.000002||Stop Cycling||1.00||0.000002|
|Bicycle Injuries||0.000154||Stop Cycling||1.00||0.000154|
|Motorcycle Deaths (Per Registered Motorcycle)||0.000689||Stop Motorcycling||1.00||0.000689|
|Motorcycle Deaths (Per Registered Motorcycle)||0.000690||Helmet Use||0.37||0.000255|
|Statin Preventable Events||0.007500||Take Statins||0.27||0.002025|
In this table, I have used the most optimistic estimates of risk reduction for some of the most widely accepted safety behaviors (e-mail me for references if you're interested) in order to demonstrate how absurd it is to marginalize statins because of their "relatively small" benefits (or costs [especially now that many are generic] or side effects [unless you have those side effects]). All of the things that we do to ensure health and safety have, on the individual level, very small benefits. But on the population level, these small absolute benefits add up - and they add up faster when the disease is prevalent and adoption is widespread.