Controls and bias

a363

I'm confused...

If a group of people, from prehistory, believe something to be true (having X will make you feel Y) and that belief affects their behaviour (when they get X, they feel Y - like a placebo - although some who do get X do not feel Y - but they are the minority), then when scientific studies are conducted (by rational members of the same group) into the effects of X on behaviour Y, it should yield results that X is strongly correlated with Y (there is no control group, everyone is exposed to the same belief and social pressure that reinforces that belief).

What will a rational member of that group conclude about the effects of x on y? How can you rationally correct for bias if there is no control?

I'm confused...

What will a rational member of that group conclude about the effects of x on y? How can you rationally correct for bias if there is no control?

(there is no control group, everyone is exposed to the same belief and social pressure that reinforces that belief)

That does not mean there is no control group. What distinguishes the treatment arm from the control arm in a placebo-controlled study is that the treatment arm receives real X, and the control arm receives mock-X, which (ideally) is indistinguishable from X. The two arms of the study are not created by finding people who have different beliefs about whether X causes Y, but by giving them X or mock-X (which is the placebo) while preventing them from knowing which one they are getting.

It seems that the OP is rather speaking about situations where the effect is purely psychological anyway, but wants to distinguish whether it is "real" or "biased". As with "having a dog will make you happy because interaction with dogs satisfies human inherent desires" vs. "having a dog will make you happy because you expect it to be the case". Even if you managed to create a mock-dog capable of fooling the subjects into thinking that it was real, it would miss the point.

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