The predictions for the LIGO detection rate are very poor.  They&#x27;re based on a sample of just a handful of binary pulsars observed in our Galaxy, which would produce NS-NS mergers.  The BH-BH merger rate is almost totally unconstrained, although it is generally thought to be less than the NS-NS merger rate.  So the fact that a BH-BH merger was the first detection, and the fact that it was detected so soon after the sensitivity increases is evidence that the BH-BH merger rate is probably somewhat higher than expected.  But we won&#x27;t know for sure until LIGO detects more events and the rate can be better constrained.  Sometimes you do just get lucky.<p>I should add that there are lots of selection biases and educated guesses in all of this, too.  The signal from BH-BH mergers is louder and easier to detect from larger distances.  At the same time, NSs are probably more common than BHs, but it&#x27;s not really clear whether there are more NS-NS binaries than BH-BH binaries because NSs receive kicks from the supernova when they are born but BHs (probably) do not.  This may have the effect of blowing apart many nascent NS-NS binaries but leaving the BH-BH binaries intact.