Sample size calculation plays an important role in bioequivalence trials. I
n practice, a bioequivalence study is usually conducted under a crossover d
esign or a parallel design with raw data or log-transformed data. In this p
aper, we discuss the differences in sample size calculation between a cross
over design and a parallel design with raw data ol log-transformed data. Fo
rmulas for sample size calculation under a crossover design and a parallel
design with raw data or log-transformed data are derived. A brief discussio
n for the relationship among these formulas is given.