Abstract:
In crossover trials, patients receive two or more
treatments in a random order in different periods. The sample
size determination is often an important step in planning a
crossover study. This paper concerns sample size calculations
in 2x2 crossover trials, with random patient effects and no
interaction between the treatment and the patient under two
scenarios, namely the exact and the large sample size approaches.
Simulation was carried out for determining the sample size for
both scenarios. For varying parameter values, simulation was
used for generating samples of the required size and examining
whether the significance level and power of the tests are
maintained. The results indicate that when the sample size was
! 5, neither method maintained error rates and when the sample
size was >5 and < 12 only the exact approach maintained error
rates. However, when the sample size is approximately > 12
both methods maintained error rates. In addition it was found
that a saving in sample size can be achieved depending on the
extent of the correlation between the observations on the same
patient. The simulation results indicate that crossover studies
should not be conducted when the anticipated sample size is
! 5 and when a sample size of >5 and < 12 is anticipated,
the exact method of determining sample size should be used.
When larger sample sizes are anticipated either method can be
used but the method based on large sample size approximation
is simpler.
