3 ms·
> If we already know what a baseline untreated group looks like There isn't really a single baseline untreated group. For a comparison between groups to be va
by jpeloquin 2y ago
> If we already know what a baseline untreated group looks like
There isn't really a single baseline untreated group. For a comparison between groups to be valid, all groups must be obtained by unbiased random sampling of the same population. In a clinical trial, that population is the patients served by the participating clinical center. Patient characteristics differ by time and place.
You can try to retrospectively construct a control group using a case control study design, but then you're getting to pick what control group to use, so the results are less reliable (more opportunity for human bias).
Unless a treatment is both miraculous in effect and works for everyone, it's hard to figure out if it works.
- mlyle 2y ago> Unless a treatment is both miraculous in effect and works for everyone, it's hard to figure out if it works. Yup. It's worth noting that "all or none" evidence is still considered category 1 evidence on many scales. (If you treat a group where all would be expected to die, and some survive... or a group where many would be expected to die, and all survive). It's only valid for the most dramatic effects, but you don't need randomization. During a safety trial you might come up with "all or none" evidence if your effect is strong enough. But otherwise, you're going to need to compare the treatment to something else. There's no ability to magically draw the exact same population from some earlier trial.