  The consistency of angle-resolved photoemission and optical conductivity
experiments on high temperature superconductors is examined. In the limit
(apparently consistent with angle-resolved photoemission data) of an electron
self energy with a weak momentum dependence and a strong frequency dependence
formulae are derived which directly related quantities measured in the two
experiments. Application of the formuale to optimally and overdoped
$Bi_{2}Ca_{2}SrCu_{2}O_{8+\delta}$ shows that the total self energy inferred
from photoemission measurements cannot be interpreted as a transport scattering
rate (in agreement with work of Varma and Abrahams), but that the inelastic
part may be so interpreted, if Landau parameter effects are non-negligible.
