Thursday, July 19, 2012

Blind luck: in praise of control groups

People often don't like the idea of "drawing the short straw" in a randomized trial. But being in the control group could turn out to be a very lucky break!

Ideally, trials are blinded so you don't know which group you're in. Knowing you're in the control group could affect your behavior and your opinions about whether or not you're benefiting (or being harmed). But even when it's not possible, it's not always fail-proof. (A placebo wasn't going to do THAT to Lisa's eyebrows!)

In theory, a trial is being done because it's genuinely not known whether the interventions being tested are better than alternatives (including doing nothing). And people who participate in clinical trials, on average, don't seem to be any worse off than people who don't - whether or not they were in a treatment or control group.

For studies that addressed this question, it was possible for researchers to get an average on experimental versus established treatments: only around half of new experimental treatments turned out to be better, and very few turned out to be a lot better. Those studies only covered about 1% of trials. Still, it's reassuring to know that people who participate in trials and end up in control groups aren't necessarily losing out.

If you'd like to read a quick introduction about control groups, go to the short sections 8.11 and 8.12 in Part 2 of the Cochrane Handbook. And here's research on blinded allocation to trials and on subjective assessment in trials.

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