Post hoc ergo propter hoc is Latin for ‘after this, therefore because of this’. The phrase refers to a common logical fallacy. An example would be ‘the rooster crows before sunrise, therefore the rooster causes the sun to rise’. Or autism follows after a measles vaccination, or a bioweapon attack on a Texas Mennonite community, therefore measles vaccines or some vastly evil and imaginary conspiracy results in autism.
A popular prohibitionist fallacy says that smoking a joint can cause someone to commit a violent act even if the violence occurs a year or more later. Despite the long history and familiarity of the post hoc fallacy, or perhaps because of it, the fallacy can also show up when news media outlets comment on cannabis.
Recently a science publication fell into post hoc fallacy territory when it revealed data linking persistent marijuana use to a higher percentage of dementia problems in medical patients five years after they had gone to an emergency ward for experiencing a bad episode using marijuana. The magic word here is “linking” because it’s possible to link anything to anything when using fallacies. The study emphasized the scope of its survey, six-million patients, although it only netted roughly16,000 examples. It is possible these patients had onset dementia without realizing it and that their adverse marijuana experience somehow highlighted it. This likelihood was not mentioned. Instead, researchers concluded with a call for more research funding for additional studies.
A CNN staff writer wasn’t satisfied with waiting for additional studies. Buried partway into an article entitled Marijuana hospital visits linked to dementia diagnosis within 5 years, study finds, the writer admits that marijuana’s link to dementia lacks a clear-cut connection, while the glaring headline and other content insinuates otherwise and keeps the question open. As presented the headline provides prohibitionists with anti-marijuana propaganda to use against legalization, at least temporarily. Big lies and deceptions have a time limit.
When dealing with topics like dementia it’s important to know who has it and who doesn’t. Just because some journalists appear to be demented nearly every time they report on marijuana doesn’t mean they are actually suffering from dementia. Other possibilities exist. A person might be suffering from mental deficiencies in Aristotle’s Rhetoric or even Wittgenstein’s Tractatus. When lacking any training in formal logic or science the media will naturally gravitate toward explanations espoused by charlatans and crystal ball gazers.
Remedies exist. Corporate news outlets and the public would benefit greatly from hiring more science-oriented reporters and personnel. The pay scale for science journalists may require a new standard. Journalism typically doesn’t attract science professionals when they can earn three times as much or more doing tech instead. To further assure truth and objectivity in cannabis reporting the news networks should be wary of allowing anyone to report on marijuana who hasn’t first tried it. Prohibitionists will need to be prohibited.
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