The increase in premium revenues beginning in 1986 reflects increases in the flat-rate premium, the addition of the variable-rate premium based on plan underfunding levels after 1987, and the phasing-out of the cap on the variable-rate premium.
The decline in premium revenue from 1996 to 2002 reflects somewhat improved plan funding and an increase in the number of underfunded plans qualifying for exemption from paying the variable-rate premium.
The increase in premium revenues in 2003 reflected deteriorating plan funding, which caused an increase in variable-rate premiums.