Animal or laboratory study | “The study was based on animals; it is impossible to know whether this treatment will work on humans or not.” |
Small study | “These results are based on a small study; larger studies are needed to understand whether the treatment works across a large population.” |
Uncontrolled study/Lack of comparator | “Everyone in this study took drug X. Without investigating patients who did not take that drug, it is impossible to know whether taking drug X accounted for the outcome.” |
Controlled but not randomised study | “The study participants were not randomized. We do not know whether it was drug X or something else that really accounted for the effect observed.” |
Important adverse event | “The benefit observed should be weighed against the adverse effects (or other downsides such as inconvenience, cost, etc).” |