Frequency of gravitational wave detection You may have heard in the news that the LIGO experiment recently detected a gravitational wave.

Though I'm not an astronomer, the paper is a good read and mostly accessible. The detection of the gravitational wave is one thing, but the black hole merger is quite new to me. From the data I could collect in the paper and this site, the source is estimated at 1.3 billion years, and the chirp lasted only a few milliseconds.  

My question: what is the frequency of events of this size order?
Is there any estimate of the density of such events in the universe?
Harry (2009) cited several different sources stated that, as far we know, the rate of detectable events will be


40 neutron star mergers per year
30 10 M$_\odot$ black hole mergers per year
10 neutron star/black hole mergers per year


This is within a radius of about 200 Mpc. This cannot, however, be used to extrapolate the total rate of such events, because of detection bias - the more massive the objects, the more easy they are to detect. The same thing happens with exoplanets, but for different reasons (e.g. planets that are more massive or closer to their stars are easier to detect via transit or by radial velocity methods).