Unless an intervention is compared to something else, it is not possible to know what would happen without it.
Without a comparison, it is difficult to say that a treatment is the reason something happened.
If people get better or worse after an intervention, you are comparing how they were after the treatment to how they were before it. The problem with such “before and after” comparisons is that you don’t know what would have happened without the intervention.
For example, if a group of people with test anxiety ate chocolate after they completed their test and their level of anxiety decreased, it might seem like the chocolate helped. However, their level of anxiety probably would have decreased after the test without the chocolate. The best way to find out if the chocolate made a difference would be to compare one group of people with test anxiety who ate chocolate to another group with test anxiety that did not – and to make sure that it was a fair comparison.
BEWARE of claims when you don’t know what the comparison was, and when they are based on before and after comparisons.
REMEMBER: Ask what the intervention was compared to, and whether it was a fair comparison.