What I tell you three times is true"

—The Bellman in The Hunting of the Snark

by Lewis Carroll

It is tempting to think that if we repeat something often enough or we repeat what others have said it will become true. Skrabanek and McCormick named this phenomenon the Bellman's fallacy in their book Follies and Fallacies in Medicine [1].

An example of this fallacy came to our attention in a recent review of the literature regarding asthma in children. In discussing explanations for the worldwide epidemic of asthma mortality in the 1960s, the author cited a previous publication [2] as follows:

"... undertreatment rather than overtreatment has repeatedly been indicated as the probable cause of the ‘epidemic’ of deaths that occurred in the United Kingdom in the 1960s."

The source of the quotation, a 1988 editorial, cited a previous review [3]:

"It is now generally accepted that excessive bronchodilator aerosol use in association with death from asthma is not a cause of death but a reflection of the need for more effective therapy".

and cited an editorial in The Lancet in 1979 [4]. "There is a growing realization that pressurized aerosols were probably not the main culprit, although excessive use of isoprenaline, as opposed to other constituents of pressurized aerosols, may have been an important contributory factor".

The 1979 editorial actually acknowledged the contributory role of isoprenaline in asthma mortality in the 1960s and discussed other hypotheses of interest [5]. Thus, the original reference presented evidence that contradicted the conclusion reached by subsequent editorialists. Once, twice, thrice, authors cited previous authors.

During the years that these sweeping statements were made (1979-1992), researchers presented data showing an association between bronchodilators (high-dose, nonselective ß agonists in particular) and the epidemics of asthma mortality. The data were collected using various study designs (ecologic and case–control studies), in different countries (Britain and New Zealand), in the general population, and in hospital-based populations. The sharp increase in deaths occurred only in the countries that licensed the high-dose, nonselective bronchodilators and ceased when these drugs were removed from the market. No evidence exists to support the unlikely speculation that sudden failure to treat asthma with steroids initiated the epidemic of asthma-related mortality occurring in only certain countries during the 1960s; it was coincident with the introduction of high-potency, nonselective ß agonists available in hand-held nebulizers.