  We compare two methods of analyzing the finite-temperature electroweak phase
transition in the minimal supersymmetric standard model: the traditional
effective potential (EP) approach, and the more recently advocated procedure of
dimensional reduction (DR). The latter tries to avoid the infrared
instabilities of the former by matching the full theory to an effective theory
that has been studied on the lattice. We point out a limitation of DR that
caused a large apparent disagreement with the effective potential results in
our previous work. We also incorporate wave function renormalization into the
EP, which is shown to decrease the strength of the phase transition. In the
regions of parameter space where both methods are expected to be valid, they
give similar results, except that the EP is significantly more restrictive than
DR for the range of baryogenesis-allowed values of $\tan\beta$, $m_h$, the
critical temperature, and the up-squark mass parameter $m_U$. In contrast, the
DR results are consistent with $2\lsim\tan\beta\lsim 4$, $m_h<80$ GeV, and
$m_U$ sufficiently large to have universality of the squark soft-breaking
masses at the GUT scale, in a small region of parameter space. We suggest that
the differences between DR and EP are due to higher-order perturbative
corrections rather than infrared effects.
