February, 2003
© 2000, 2001 Scott S. Emerson, M.D., Ph.D.
Flexible
methods compute boundaries at an interim analysis according to study time
at that analysis
Study time can be
measured by
·Proportion
of planned number of subjects accrued (maintains maximal
sample size)
·Proportion
of planned statistical information accrued (maintains
statistical power)
·(Calendar
time-- not really advised)