|In a controlled exposure study, one group
of participants is exposed
to a substance (e.g. a pollutant) while those in
the "control" group are not. The results
are then compared to determine the health effects
of the substance being studied.
In a placebo controlled study (often called
simply controlled study), people in the
"treatment" group are given the drug
or treatment being tested while the control group
receives a placebo
or a different treatment.