A recent online health service noted: “40% of cancers are due to avoidable life choices… Tobacco causes 23% of [cancer] cases in men and 15.6% of cases in women. The next largest cause of cancer in men was lack of fruits and vegetables in their diets…”
Hold it right there! When someone says that a certain activity “causes” another event to occur, it should be backed up by some very good studies in one of two ways. One method is for a group of people to be given activity A and to be watched for specific result B, and then the same group of people not to be allowed activity A and again watched for result B.
Or (as in the case of smoking or eating fruits and vegetables where the time is too long for the appearance of cancer and the appearance of cancer cannot be taken away in order to do the second phase of the study) two groups of people, as alike as possible (to rule out other causes), are selected, one of which is given activity A and the other group is not, then both groups are watched for result B.
As you can imagine, it is impossible and probably unethical to have one group of people specifically smoke or one group of people specifically not eat fruits and vegetables just to see if they get cancer. The next best thing is to find groups of people as alike as possible (to rule out other interfering variables) one group of which already does and the other group already does not do activity A, then watch them over time to look for result B.
The less desirable study is to find people who have suffered result B and to compare them to people who have not suffered result B, trying to isolate what activities are different about those who did and those who did not suffer result B. Comparing groups of people to each other or to information gathered on the population in general is the stuff of epidemiology, an attempt to ferret out possible relationships between known activities and observed results. The epidemiologist is looking for probable “cause.”
But these kinds of studies do not prove “cause.” Just because a person does activity A and gets result B does not mean that A caused B. There might be another activity C (which might or might not be related to activity A), that activity A people were also doing, which caused result B. While statisticians try to eliminate these possibilities with statistics, epidemiologic studies cannot prove that activity A “causes” result B.
Be careful! Don’t just dismiss these studies. Pay attention, because they tell us and the researchers where to go looking for probable cause. While in some cases (like making people smoke to see if they get cancer) these studies cannot be done in people, the studies are done in animals that closely approximate people and the results theorized to have the same effect in people.
“Over 6 years, Spanish researchers found that those who ate the most fast foods and processed pastries were 37% more likely to develop depression.” Does eating fast food “cause” depression? Does that make any sense? People who have a stressed life style, who are pressing for time and demanding perfection in the work place, who have no time to prepare healthy food, might also be prime setups for depression, especially if they don’t succeed or burn out prematurely. But there is no direct causal link between fast foods and depression, as the authors of the article did point out.
“Each 4 point increase in BMI (being overweight), increases the risk of heart disease by 52%.” Does this make sense? The researches went on to say that “higher BMI influences well-known risk factors like hypertension and type-2 diabetes.” The researchers note that BMI (activity A) influenced activities C and D which are known to “cause” heart disease (result B).
When you read the studies or hear them on the news, ask yourself – “does this make sense?” Did they prove that activity A actually “causes” result B? Or is there just a suspicion and more well-controlled studies are called for? Read carefully and thoughtfully. Don’t assume causality. But don’t ignore the warning either.
