00:00Studies have shown that taking vitamins is good for your health
00:10and bad for your health.
00:12That newly discovered herb can improve your memory
00:15or destroy your liver.
00:16Headlines proclaim a promising new cancer treatment
00:19and never mention it again.
00:21On a daily basis,
00:22we are bombarded with attention-grabbing news
00:24backed up by scientific studies.
00:26But what are these studies?
00:27How are they performed?
00:28And how do we know whether they're reliable?
00:30When it comes to dietary or medical information,
00:33the first thing to remember is that while studies on animals
00:36or individual cells can point the way towards further research,
00:39the only way to know how something will affect humans
00:42is through a study involving human subjects.
00:44And when it comes to human studies,
00:46the scientific gold standard is the randomized clinical trial, or RCT.
00:51The key to RCTs is that the subjects are randomly assigned
00:54to their study groups.
00:55They are often blinded to make them more rigorous.
00:57This process attempts to ensure that the only difference between the groups
01:01is the one the researchers are attempting to study.
01:04For example, when testing a new headache medication,
01:06a large pool of people with headaches
01:08would be randomly divided into two groups,
01:10one receiving the medication and another receiving a placebo.
01:14With proper randomization,
01:15the only significant overall difference between the two groups
01:18will be whether or not they received the medication,
01:21rather than other differences that could affect results.
01:24Randomized clinical trials are incredible tools,
01:27and in fact, the U.S. Food and Drug Administration often requires at least two to be conducted
01:32before a new drug can be marketed.
01:34But the problem is that an RCT is not possible in many cases,
01:38either because it's not practical or would require too many volunteers.
01:42In such cases, scientists use an epidemiological study,
01:46which simply observes people going about their usual behavior,
01:49rather than randomly assigning active participants to control and variable groups.
01:53Let's say we wanted to study whether an herbal ingredient on the market causes nausea.
01:58Rather than deliberately giving people something that might make them nauseated,
02:01we would find those who already take the ingredient in their everyday lives.
02:05This group is called the cohort.
02:07We would also need a comparison group of people who do not have exposure to the ingredient,
02:11and we would then compare statistics.
02:14If the rate of nausea is higher in the herbal cohort,
02:16it suggests an association between the herbal supplement and nausea.
02:20Epidemiological studies are great tools to study the health effects of almost anything,
02:25without directly interfering in people's lives,
02:27or assigning them to potentially dangerous exposures.
02:30So why can't we rely on these studies to establish causal relationships
02:33between substances and their effects on health?
02:35The problem is that even the best conducted epidemiological studies have inherent flaws,
02:40precisely because the test subjects are not randomly assigned to their groups.
02:44For example, if the cohort in our herbal study consisted of people
02:48who took the supplement for health reasons,
02:50they may have already had higher rates of nausea than the other people in the sample.
02:55Or the cohort group could have been composed of people who shop at health food stores,
02:59and have different diets, or better access to health care.
03:02These factors that can affect results in addition to the factor being studied
03:05are known as confounding variables.
03:08These two major pitfalls, combined with more general dangers,
03:11such as conflicts of interest or selective use of data,
03:13can make the findings of any particular epidemiological studies suspect,
03:17and a good study must go out of its way to prove that its authors have taken steps
03:21to eliminate these types of errors.
03:23But even when this has been done, the very nature of epidemiological studies,
03:27which examine differences between pre-existing groups,
03:29rather than deliberately inducing changes within the same individuals,
03:32means that a single study can only demonstrate a correlation
03:36between a substance and a health outcome,
03:38rather than a true cause and effect relationship.
03:41At the end of the day, epidemiological studies have served
03:44as excellent guides to public health,
03:46alerting us to critical health hazards such as smoking, asbestos, lead, and many more.
03:51But these were demonstrated through multiple,
03:53well-conducted epidemiological studies, all pointing in the same direction.
03:57So the next time you see a headline about a new miracle cure,
04:00or the terrible danger posed by an everyday substance,
04:03try to learn more about the original study and the limitations
04:06inherent in any epidemiological study or clinical trial
04:09before jumping to conclusions.
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