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The “blue-ribbon” version of the individual experimental study
is the randomized control trial (RCT). This study is like a
cohort study with two or more groups followed up to see if
the outcomes are different. But in this kind of study,
individuals are randomly allocated to one treatment or another;
and when the results are analyzed, the first analysis is to see
if the two groups are comparable in demographic and other
variables, as they should be after random allocation. If this
is so, then the differences in outcomes from the treatments can
be ascribed to the treatments rather than to differences in the
individuals in the groups.
An alternative to this methodology is to conduct a cross-over
study in which the individuals receive both treatments: Group
A receiving Treatment A first and Treatment B second, and Group
B then reverse. This, of course, may not be feasible if surgical
removal of an organ is one of the treatments, or if the condition
is life threatening.
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