  Supplemental information for a Letter reporting the rate of binary black hole
(BBH) coalescences inferred from 16 days of coincident Advanced LIGO
observations surrounding the transient gravitational wave signal GW150914. In
that work we reported various rate estimates whose 90\% credible intervals fell
in the range $2$--$600 \, \mathrm{Gpc}^{-3} \mathrm{yr}^{-1}$. Here we give
details of our method and computations, including information about our search
pipelines, a derivation of our likelihood function for the analysis, a
description of the astrophysical search trigger distribution expected from
merging BBHs, details on our computational methods, a description of the
effects and our model for calibration uncertainty, and an analytic method of
estimating our detector sensitivity that is calibrated to our measurements.
