I coined this name for it after having an exchange with Dr. John McDougall, M.D., in the comments on my post Dr. McDougall on B12. In response to my post, Dr. McDougall stated:
"Clinically significant diseases due to dietary B12 deficiency are so rare that they appear as case reports in medical journals, and then do so very infrequently. Thus, with millions of vegans worldwide and a handful of reported cases of clinical disease, I derived the estimate of fewer than one in a million risk."This exemplifies the Iceberg Fallacy. Dr. McDougall assumes that no one has suffered a clinically signficant disease due to dietary B12 deficiency except the "handful of reported cases of clinical disease" found in medical journals. As I pointed out in response:
"Your estimate of the incidence of B12 deficiency related disease suffers from the problems of survivor bias and reporting bias. Reporting bias because not every incident of illness arising from vegan diet or B12 deficiency gets reported to any central database from which you can draw to make an accurate estimate of the incidence of such diseases. In fact, people who feel ill from vegan diets (as I did during the 12 years I avoided animal products) generally just end up discontinuing the diet, never to return and without reporting their adverse experience to any physician or database. This is especially true of vegans in isolated rural areas of India, China, etc. [Edit: who don't even have access to physicians or databases.] Survivor bias emerges in developed nations; the people who continue eating vegan diets for long periods of time are "survivors" of a deficient diet, people who apparently have lower requirements for B12, iron, zinc, or whatever, or are among the people capable of converting carotenes to retinol (see below). You may not find deficiency-related diseases among these long-term vegans because they are the ones who tolerate the lower nutrient delivery of a vegan regime, or they use isolated nutrient supplements (multivitamin or minerals) [or fortified foods] regularly, thereby masking the deficiencies of their diet."This conversation reminded me of a statement attributed to Confucius, and another similar passage from the Tao Te Ching. I paraphrase Confucius (because I don't have the text readily available): To know that you do not know, that is true knowledge. I quote the Tao, chapter 71 (Wu translation):
To realize that our knowledge is ignorance,
This is a noble insight.
To regard our ignorance as knowledge,
This is mental sickness.
Only when we are sick of our sickness
Shall we cease to be sick.
The Sage is not sick, being sick of sickness;
This is the secret of health.
The mind easily assumes that reality contains only what it "knows," forgetting that its ignorance far exceeds its knowledge. The mind tends to focus on the foreground, and ignore the background. Hence, it easily commits the Iceberg Fallacy, by assuming that nothing exists except the obvious (the tip of the iceberg) or the documented. By ignoring the submerged part of the iceberg, or the unknown, it gets itself into a lot of trouble.
If you assumed that no thefts happened yesterday except those that got reported in the newspapers, you would commit the same Iceberg Fallacy. Probably, on any single day, more thefts occur than get noticed, and more thefts get noticed than get reported. Similarly, in any time period, most likely more diseases due to B12 deficiency occur than get noticed by medical professionals, and more get noticed by professionals than get reported in medical journals.
To wrap, if the mind sees only a few case reports of disease due to B12 deficiency of vegans in the medical literature, the most one can validly conclude is that very few cases of B12 deficiency disease due to vegan diets have actually gotten reported and published in the indexed medical literature. You can't validly conclude that only those few cases have occurred.
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