Control Groups and why they matter
(Also why we sometimes don’t use them and why that can be valid)
Science Literacy Lesson #3
Let’s say you have a brand new product that you think is wonderful (a new pet diet, an essential oil treatment, a new human antiviral, etc) and you want to do an experiment to prove it to the world.
You give it to a bunch of test subjects and 60% of them improve in whatever you’re measuring (pet health, anxiety, and patient survival in these examples). That’s great right? Proves it works?
Nope! Completely meaningless without a control group to compare it to.
You might have a hypothesis that your variable (the new food, treatment, medicine, etc) is effective, but you need to prove it against a population without that variable.
The saying in medicine is that about 2/3 of patients will recover no matter what you do. So it’s really, really important to know that a treatment you are recommending, or the variable you are testing in this experiment, performs better than ‘literally nothing’.
That’s where your control group comes in. If you gave 50 participants your experimental variable (food, essential oil, antiviral etc) and 30 improved in whatever you were measuring, but you also have a group of 50 participants that you didn’t give it to and 30 of them also improved, then your product is not as good as it initially looked.
So what might constitute a ‘control’ group?
An ideal control group receives no treatment. For some types of tests that’s not completely feasible as subjects are aware of whether they’re taking a pill or not, so that’s where a placebo is used. Both subjects are taking a pill, but only one is real and the other is known to produce no measurable results.
Using a placebo for the control group is ideal for something like the essential oils example, because you are testing an active product against nothing. You want to know whether that essential oil has any better results than the placebo.
This gets a little harder when testing a diet, because you can’t feed your control group literally nothing. Obviously the group being fed literally nothing for 12 months will be worse off than the group being fed the experimental diet! You have to feed them something, and this would either be a ‘market leader’ diet or an equivalent diet without the one variable you are trying to test (protein level, specific ingredient, etc).
Testing medicines, especially in humans, can get tricky again, especially if you’re testing a treatment for something critical where patients who are untreated are likely to die or suffer. So for these types of experiments the control group will be given the current standard treatment to see how that compares to the experimental one, instead of no treatment at all. You can’t ethically not treat your cancer/pain patients because they were randomly assigned to a control group.
And specifically in medical experimental trials, some will have a type of escape clause where if the tested medicine is proving amazingly, super effective, to the point where it would be definitely cruel to deny the control group that treatment, the control group is sort of disbanded and given the treatment anyway. This is one of the few situations where it’s acceptable to not have a control group. You had one, but they were doing so much worse than the experimental group that it wasn’t fair for them to continue.
Next time: Placebos, blinding and reporting bias
















