PLOS ONE: study on the increase in scientific retractions

Following on from their previous research on research integrity, R. Grant Steen, Arturo Casadevall and Ferric C. Fang ask why number of scientific publications being retracted has risen sharply? Is it because flawed articles are being retracted more quickly or has there been an increase in the number of flawed articles being published?

The study is available from PLOS ONE:

PLOS ONE: Why has the number of scientific retractions increased?