See updated History of Medicare Conversion Factors.
Initially, the Medicare Physician Fee Schedule included distinct conversion factors for various categories of services.
In 1998, a single conversion factor was offset by elimination of the work adjustor and increases in practice expense (PE) and professional liability insurance (PLI) relative value units (RVUs).
The reduction in the 2009 conversion factor was offset by elimination of the work adjustor from the third 5-Year Review (2007; 0.8994 rounded to 2 decimal places).
The reduction in the 2011 conversion factor was offset by increases to PE and PLI RVUs resulting from the rescaling of those RVU pools to match revised Medicare Economic Index weights.