When clinicians diagnose disease, they are inevitably involved in questions of cause and effect. To treat effectively depends on understanding pathogenesis and etiology – that is causation, which is often the first thing that comes up in office visits.
Most patients, when they face an illness, want to know “why?” or even “why me?” Most times, despite these questions, they may already have arrived at their own causation theory, often involving a time sequence.
Family doctors, more than any other clinicians, cite behaviour as a self-inflicted cause for health problems but, when saying anything about habits or diet, some patients can feel defensive because … it is their “fault”.
Correlation or causation
Correlation does not imply causation as events that coincide are not necessarily causally related. Reality is that cause and effect can be due to a third factor, or entirely coincidental. The assumption of causation is false when the only evidence available is simple correlation.
People generally get to the easier conclusion: “After this, therefore because of this.”
We experience the world in a time-oriented manner through cause and effect. Often, it seems absolutely clear that a specific action caused a second event to happen. This is what is known as causation.
After something especially beneficial or harmful occurs, we want to know what caused it. We tend to focus on the first action we noticed before the effect, assuming that it must have been what triggered the later event.
Searching for certainty
It is irresistible to make an association between two events that occur together but even if these associations are often right, sometimes they are wrong and can cause harm.
A poorly designed study published in the Lancet in 1998 proposed an association between the measles vaccination and autism. The study was retracted in 2010 but, in the meantime, tens of thousands of parents decided to leave their children unimmunised.
This anti-vaccine movement was considered to be responsible for an outbreak of measles that occurred at Disneyland.
We clinicians are always revising our ideas about association and our theories of causation in light of new evidence, although sometimes new evidence affirms traditional ideas.
Establishing a definitive cause can be difficult. What is primary and what is secondary? Many difficult patients present with “chicken and egg” scenarios.
Someone comes in urinating a lot: Is it diabetes insipidus making them thirsty, as they suspect? Or is the patient drinking a lot because he read somewhere that drinking eight glasses of water a day was a good idea to stay hydrated?
Cause and effect
What does all of this mean for us as clinicians? We search for the etiology of disease, but often we cannot assign an ultimate cause. Some cancers have environmental or genetic triggers, but the majority do not. This is very unsatisfying; we want to know the cause so we can treat, prevent or eradicate a disease. Separating apparent causes from real ones demands that all of the available evidence is considered.
In 1965, the strong association between smoking and lung cancer was sufficient evidence for the health authorities to issue a public warning. Tobacco company lawyers argued for 40 years that smoking merely “correlated” to lung cancer rather than actually caused it.
The problem is that correlation is different from causation. Correlation is when two or more things or events tend to occur at about the same time and might be associated with each other, but are not necessarily connected by a cause/effect relationship.
Cell phones and alligators
In 2003, a Hungarian medical study of 221 men found that men who carry cell phones in the front pockets of their trousers had a 30% lower sperm count than the average male population. Immediately lawsuits started against cell phone companies for causing sterility in men, and some consumer watchdogs called for warning labels on cell phones.
Reality is that this study found correlations but did not determine clear causation. In fact, smokers carried their cigarette pack in their jacket pockets to avoid crushing their cigarettes and thus carried the cellphone in their trousers instead.
It has long been known that smokers have a reduced sperm count. Perhaps smoking caused the lower sperm count, not the position of the cell phone. Other factors like stress levels can also cause a drop in sperm count and the overall sperm count of men has dropped from the 1970s, as a whole, possibly due to the increasing levels of chemical pollution worldwide.
Male alligators in parts of Florida also have 30% lower sperm counts than they did in the 1970s, but nobody thinks that is a result of their cell phone use!
Doctors want to cure, to prevent, to stop disease. To do this they need to find out why – at least to try – objectively.
The search for cause, among doctors and patients alike is, in some sense, a search for control. The whole concept of luck, good or bad, is alien to the medical thinking. Doctors, like their patients, want to know why.
Best healthy wishes,
Dr. Maria Alice
Dr Maria Alice
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Dr Maria Alice is a consultant in General and Family Medicine. General Manager/Medical Director – Luzdoc International Medical Service / Medilagos. Medical Director – Grupo Hospital Particular do Algarve