We present a least squares method for estimating parameters from measurements
of event yields in the presence of background and crossfeed. We adopt a unified
approach to incorporating the statistical and systematic uncertainties on the
experimental measurements input to the fit. We demonstrate this method with a
fit for absolute hadronic D meson branching fractions, measured in e+e- ->
\psi(3770) -> D\bar D$ transitions.Comment: 9 pages, 2 figures; minor clarifications, one figure adde