February, 2003
© 2000, 2001
Scott S. Emerson, M.D., Ph.D.
Choice of P
parameter
P ³ 0:
· Larger positive values of P make early stopping
more difficult (impossible when P infinite)
·When A=R=0, 0.5
< P < 1 corresponds to power family parameter (D) in Wang &
Tsiatis (1987): P= 1 - D
·Reasonable
range of values: 0 < P < 2.5
·P=0 with
A=R=0 possible for some (not all) boundaries, but not
particularly useful