Researchers attempting to evaluate the effectiveness of a
treatment frequently suffer from difficulty finding enough
people who are willing to participate in a study. One method
used to address this common problem is called the crossover
study. Crossover studies are usually also double-blind studies.
In the ordinary form of a double-blind study, participants
receive either a real treatment or a placebo for the duration of
the trial. A study of this type is said to have "parallel-group
design." In a double-blind, crossover study, however,
participants receive either real treatment or placebo for a
time, and then are switched ("crossed over") to the opposite
treatment. Thus, researchers can get double mileage out of their
participants—each person gets both placebo and treatment. The
advantage of a crossover trial is that it effectively doubles
the number of people in a trial. This makes it easier for
researchers to obtain statistically significant results.
However, there are some major disadvantages with crosso