Placebos and controls in research - (Jul/16/2008 )

Dear all,

Are there differences between a control and placebo in an experiment? Especially one that involves animal instead of human. Since placebo is used to reduce variability that may arise as a result of psychological response to a treatment, I believe it doesn't work on a rats right?

I have came across researchers using placebo AND control in an experiment to test the efficacy of a topical compound on hair regrowth in rats.

Two cents please?

Cheers.

The placebo in those experiments was probably the drug formulation with out the active ingredient. The control may have been untreated entirely.
The reason for doing both placebo and untreated controls may have been to see if the topical ointment (minus drug) had any positive or negative effect on hair growth.

At my previous job, we did mouse tumor studies with placebo controls only. The mice were too expensive to do two negative control groups.

Thanks rosewater and NTH for the replies. I take it that the use of placebo and control is very much up to the one carrying out the experiment as well as the cost of the whole thing.

The terms in casual use are prob interchangeable but i think placebo is most commonly considered in trials where the subject's cognizance or expectation of a potential effect may confound observation. In clinical studies(some preclinical as well) you may not have (negative) controls or placebos as such. The active ingredient being evaluated may be so characteristic that you can't hide it (DMSO for arthritis) or ethics demand that you not leave a test population untreated. For some of these, you might compare to another effective treatment).

Ok. Thank you jorge1907