Truth Decay

Truth Decay is the title of an intriguing and important article in the New Scientist.1 The author writes that when his grandfather was in dental school he learned that there were 48 chromosomes in a human cell. This was regarded as an established fact. But in 1956 Joe Hin Tjio and Albert Levan discovered using an improved and more accurate technique that there were only 46 chromosomes in a human cell.

It is the nature of science that facts change. Scientometrics is the field that studies how these facts change. The rate of change will likely surprise you. Thierry Poynard and his colleagues measured the churning of facts in two medical fields in which they specialized. Cirrhosis and hepatitis are two liver diseases. They took almost 500 articles in these fields from over a period of 50 years and gave them to a panel of experts to review. Each expert needed to rate each paper as to whether it was factual, out-of-date, or disproved.2 They discovered that 45 years after publication, 50% of journal articles had effectively decayed. They concluded that these articles had a 45 year “half-life.” Another study came to the same conclusion in a review of studies on surgery.3

The above studies were extremely pain-staking to conduct, so another method is used, and that is how long it takes for researchers to stop citing the average paper in the field. This technique is not as good as the failure to cite a paper does not necessarily indicate that the findings of the paper are no longer true. It could be that there are more recent and up to date papers, or that the journal’s focus has moved on to other topics. Nevertheless, this technique does provide an approximation. A study of Physical Review journals found that the half-life in physics is about 10 years.4 Half-lives also vary as a function of publication formats for different fields. In a study of scholarly books, physics has a different half-life (13.7 years), economics (9.4 years), which is longer than half lives of mathematics, psychology, and history.5 However, in journal articles, as opposed to scholarly books, the frontiers of hard science are overturned more rapidly than the frontiers of the social sciences.

The estimates of half lives and the rates of turn over in different publications and in different fields, although interesting, are not the main point here. The main point is that facts change and they change rapidly. For many years the Prostate Specific Antigen (PSA) was strongly recommended for all men over a certain age. Now it is only recommended for high risk groups and even then, only after consulting with their physician. I have been through many different ideal food groups in my life. At one time dairy products were supposed to be nature’s most perfect food. At another time the US had four basic food groups. Then there was a food pyramid that underwent multiple changes. Now there are five food groups. Advice on the consumption of fatty foods, carbohydrates and many other things change.

The purpose of this blog post is not to discredit science. At any given time, science provides the best facts for that time. But science is in constant flux, and what is factual today might not be factual at some future date. So remember that some of what you learned during your formal education might not be true today. This underscores the importance of lifelong learning, and lifelong learning fosters healthy memories.

1Arbesman, S. (2012). Truth Decay. New Scientist, 22 September, 37-39.

2Annals of Internal Medicine, Vol 136, p.888).

3The Lancet, vol 350, p.1752.

4Arxiv.org/abs/physics/0407137.

5College and Research Libraries, vol 69, p 356.

© Douglas Griffith and healthymemory.wordpress.com, 2012. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Douglas Griffith and healthymemory.wordpress.com with appropriate and specific direction to the original content.

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