In December, 2011, the New York Times published an article estimating that one-third to two-thirds of non-engineered earthquake retrofits in the San Francisco Bay Area are installed incorrectly. (See the article here: http://www.nytimes.com/2011/12/23/us/seismic-retrofits-offer-shaky-assurance-in-california.html?pagewanted=all&_r=0) In 2006, the Contra Costa Times estimated that 69% of retrofits would not function as expected.
The Golden Gate Chapter of the American Society of Home Inspectors did an informal poll of its members, who estimated that only one in ten retrofits will be fully effective. This is another reason that building owners need to get engineers involved in seismic retrofitting project instead of relying on specialty contractors.