Is Epidemiology Worthless?

Epidemiology has lots of critics. In this article, for example, it is called “lying on a grand scale.” Every critique I have read has ignored history. Epidemiologists have been right about two major issues: 1. Heavy smoking causes lung cancer. 2. Folate deficiency causes birth defects. In both cases, the first evidence was epidemiological. Another example is John Snow’s conclusion about the value of clean water. In my experience, epidemiologists often overstate the strength of their evidence (as do most of us) but overstatement is quite different from having nothing worth saying.

Let’s look at an example. Many people think osteoporosis is due to lack of calcium. Bones are made of calcium, right? The epidemiology of hip fractures is clear. In spite of the conventional idea, the rate of hip fracture has been highest in places where people eat a lot of calcium, such as Sweden, and lowest in places where they eat little, such as Hong Kong. (For example.) In other words, the epidemiology flatly contradicted the conventional idea. This was apparently ignored by nutrition experts (everyone knows correlation does not equal causation) who advised millions of people, especially women, to take calcium supplements  to avoid osteoporosis. Millions of people followed (and follow) that advice.

Thanks to a recent meta-analysis we now know that experiments and better data firmly support the earlier epidemiology, which suggested that calcium supplements are dangerous. Here are its main conclusions:

In meta-analyses of placebo controlled trials of calcium or calcium and vitamin D, complete trial-level data were available for 28,072 participants from eight trials of calcium supplements and the WHI CaD participants not taking personal calcium supplements. . . .Calcium or calcium and vitamin D increased the risk of myocardial infarction (relative risk 1.24 (1.07 to 1.45), P = 0.004) and the composite of myocardial infarction or stroke (1.15 (1.03 to 1.27), P = 0.009). . . . A reassessment of the role of calcium supplements in osteoporosis management is warranted.

If the epidemiology had been taken more seriously, many heart attacks might have been avoided.

Is this an “anecdote” — a single example — proving nothing? Here’s how you can check. Randomly select a meta-analysis of epidemiological studies. Thousands have been done. Then ask if the results summarized in the meta-analysis appear random. Better yet, randomly pick two meta-analyses. Suppose the first summarizes 5 studies and the second summarizes 6. If the 11 results were shuffled together, how well could you assign them correctly?

Seth Roberts is a professor of psychology at Tsinghua University and an emeritus professor of psychology at the University of California Berkeley. This piece is reposted from his blog.

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7 replies »

  1. Sir:

    The World Health Organization has published a recommendation that ALL
    drinking water on earth contain at least 25 mg of Magnesium per liter to
    prevent heart attacks and strokes (now estimated at 4.5 Million deaths
    per annum). (recommendation written by my friends Dr. Burton Altura and
    Dr. Bella Altura; and global estimate written by my friend Dr. Andrea

    The NAS estimated American deaths from magnesium-deficient water to be
    150,000 per annum — back in 1977.

    Now I want to help fund a large scale Clinical Trial, of adding 100 mg
    of Magnesium per liter of drinking water, both tap and bottled, to
    controlled populations having good medical records to record heart
    attacks, strokes, violence, and deaths. Such controlled populations
    might include prisons, VA Hospitals, and remote villages.

    Can you introduce me to people who might work with us?

    I set up the Magnesium Online Library about 15 years ago, and funded it,

    Perhaps in Feb. 2015 I could start funding $10,000 per month for a new
    non-profit Foundation, which might be called Critical Mg Trials
    Foundation. In addition to the scientists I already partially fund.


    Paul Mason, Mg Librarian

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  4. Sir:

    How does “Heavy smoking cause(s) lung cancer”, exactly?



  5. I am also confused, but I think it’s rather from the OP’s lack of clarity (” Then ask if the results summarized in the meta-analysis appear random. “). Is that the same scholar who recently wrote friendly here about self experimentation?

  6. I’m confused. How does the epidemiology of calcium intake and hip fracture, which seems to indicate that calcium is not protective for hip fracture, show anything about whether calcium supplements cause MI and stroke?