Common pitfalls underlying cause-and-effect relationships


In the realm of medicine, cause-and-effect relationships are those where a specific cause, such as a disease, condition, or treatment, directly leads to a specific outcome or effect. An example of this is the established fact that smoking causes lung cancer. Similarly, it is well-documented that regular, heavy alcohol consumption directly leads to liver cirrhosis.

On the other hand, phrases like “associated with,” “linked to,” and “tied to” denote a correlation or relationship between two factors but do not definitively establish causality. For instance, a sedentary lifestyle is often associated with heart disease. This means that a higher incidence of heart disease is observed in people who lead a sedentary lifestyle, but it does not necessarily establish that a sedentary lifestyle is the direct cause of heart disease. Other factors may also contribute to the development of this condition.

Similarly, high-stress levels are linked to insomnia. Although people with high-stress levels often suffer from insomnia, it is not definitively proven that stress is the direct cause of insomnia, as other factors could also be involved. We might also say that high sugar consumption is associated with obesity. While there is a correlation between the two, it cannot be definitively said that high sugar consumption is the sole or primary cause of obesity, as there are many other contributing factors, such as physical inactivity, genetics, and other dietary habits.

Therefore, the difference between cause and effect and phrases like “associated with” and “tied to” essentially lies in the strength and certainty of the relationship. Cause and effect indicate a direct and certain relationship, while “associated with” and “linked to” indicate a correlation or consistent relationship but not necessarily a direct causal one.

Historically, there are several notable examples where cause-and-effect relationships in medical science were later proven to be incorrect. One such example is the miasma theory, which proposed that diseases like cholera and the Black Death resulted from “miasma” or bad air. This theory was eventually replaced by the germ theory of disease, which identified specific microorganisms as the true cause of these illnesses.

Another misconception involved stomach ulcers. For a long time, stress and spicy foods were believed to be the primary cause of these ulcers. However, this understanding was revolutionized in the 1980s when two Australian scientists discovered that the bacterium Helicobacter pylori was actually responsible for most stomach ulcers, not stress or diet.

A more recent and well-known example involves the alleged link between the MMR vaccine (measles, mumps, rubella) and autism. In 1998, a study suggested this link, leading to widespread fear and a drop in vaccination rates. However, the study was later retracted due to serious procedural errors, undisclosed financial conflicts of interest, and ethical violations. Numerous subsequent studies have consistently found no connection between the MMR vaccine and autism.

The safety of Gardasil has also come into question. Gardasil is a vaccine, and the only one given to protect against human papillomavirus (HPV) in the U.S. HPV is the most common sexually transmitted infection among women and a known cause of genital warts and cancer later in life. The FDA and CDC refute that the vaccine causes cancer, as individuals have claimed in lawsuits against Gardasil’s manufacturer, and no studies have found any association between the HPV vaccine and autoimmune conditions, as plaintiffs have also alleged. Litigation is ongoing.

There has been continuing debate and research into whether living near cell phone towers or high-voltage power lines can increase the risk of cancer. The concern arises from the fact that both cellphone towers and power lines emit low-level radiofrequency (RF) energy, a type of non-ionizing radiation.

Non-ionizing radiation is generally considered less harmful than ionizing radiation (like X-rays or radon), which has enough energy to damage DNA and potentially lead to cancer. However, the question is whether long-term exposure to low-level non-ionizing radiation can still have harmful effects.

The World Health Organization (WHO), based on the current body of scientific evidence, states that exposure to low-level RF fields, like those emitted by mobile phones and their base stations, is not harmful to human health. Similarly, many studies have found no consistent evidence that living near high-voltage power lines increases the risk of leukemia or other cancers.

However, research in this area is ongoing and evolving. The WHO’s International Agency for Research on Cancer (IARC) has classified RF fields as “possibly carcinogenic to humans” based on limited evidence from human studies and less than sufficient evidence from lab studies.

In conclusion, while the current body of evidence suggests that living near cellphone towers or high-voltage power lines does not increase the risk of cancer, more research is needed to definitively answer this question.

These examples underscore the importance of rigorous scientific research and evidence-based medicine. They remind us that our understanding of medical cause-and-effect relationships can change and evolve based on new evidence and that rigorous study design, peer review, and replication of results are crucial in ensuring reliability and validity in scientific research.

Journalists often rely on the information and language used in scientific research studies, and they commonly use phrases like “associated with” and “linked to” when writing headlines. This can sometimes contribute to misunderstandings about scientific research and the role of causation in the findings.

The Association of Health Care Journalists’ guidance on covering research studies actually aims for wording that suggests a less direct relationship. Creating headlines can be challenging, as journalists need to strike a balance between accurately conveying the nuances of scientific research and making the information accessible and understandable to a broad audience.

The phrase “lies, damned lies, and statistics” is often attributed to Mark Twain, who used it in his autobiography. However, Twain himself credited it to British Prime Minister Benjamin Disraeli, although there’s no record of Disraeli using the phrase.

The phrase suggests that statistics can be manipulated or misrepresented to support any argument, even a false one. It underscores the idea that while statistics can be powerful tools for understanding data and trends, they can also be misused to mislead or confuse individuals and demonstrate causality when none exists. The phrase serves as a cautionary reminder to critically evaluate statistical claims and to consider the source of data and methodology before assuming cause and effect.

Arthur Lazarus is a former Doximity Fellow, a member of the editorial board of the American Association for Physician Leadership, and an adjunct professor of psychiatry at the Lewis Katz School of Medicine at Temple University in Philadelphia, PA. He is the author of Every Story Counts: Exploring Contemporary Practice Through Narrative Medicine, Medicine on Fire: A Narrative Travelogue, and Narrative Medicine: The Fifth Vital Sign.


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