It seems that just about every case study one reads, especially about nutrient deficiency-induced illness or medication-induced side effects, begins with the premise that such events are rare. This is not based upon any mathematical concept of infrequency derived from solid data. Nope, that would be entirely too logical. Rather, these proclamations of rareness are often based upon two suppositions: 1) the practicing physicians have not personally seen such cases, and hence, the desire to publish the case in the first place, and 2) the literature tells us these cases are rare, because every ‘rare’ case that is published is denoted as being rare in the introduction. If these two conditions are met, then it must, in fact, be rare.
Is it though? If we have never measured a particular nutrient or assessed the frequency of a particular side effect in our patient populations, can we really assert that what we have discovered in a particular patient is in fact, rare? It is entirely possibly that if one were to measure these variables in each and every patient one sees, that the deficiencies or side effects would present quite regularly. It is a logical fallacy to assume that somehow our ignorance of said effects proves those effects do not exist. That is precisely what happens though in the case literature, but also, in much of the research and meta-analyses of those studies. It is as though if we say something is rare often enough, it becomes the overarching truth, no matter the lack of actual data to support the claim. By way of example, I challenge you to find any case report that does not begin with some derivation of ‘X is rare’.
In my area of research, thiamine deficiency, here are just a few examples.
“A severe depletion is not commonly seen, except in cases of inadequate nutrition and/or alcoholism.”
“Cardiac beriberi, or heart failure due to thiamine deficiency, is considered rare in the developed world.”
“Thiamine deficiency is rare in developed countries and is most commonly associated with chronic alcoholism. The other predisposing conditions include chronic dietary deprivation and impaired absorption or intake of dietary nutrients.”
“Nowadays, in the developed world, it is relatively rare.”
Indeed, search the case and research literature on just about any nutrient deficiency and you will see the same assertions of rareness. Ditto for medication side effects. Read enough of these reports and one might think that we are a population of super healthy individuals who suffer no chronic illness and experience no side effects from any medication or vaccine.
I suppose if one ignores the data showing that 50% of the population lives with at least one chronic illness, generally of metabolic origins, and 27% have multiple, then sure, we can consider all of this rare, especially if one falls for the logical fallacy that an absence of evidence equates evidence of absence. Is it really, though? I cannot help but wonder if the assertion of rareness is a collective salve to save ourselves of the embarrassment of not ever having looked; a hear no illness, see no illness, speak no illness approach to medicine.
Can something be rare if it is never measured? Is it really rare or simply rarely measured?
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