The “funded ratio” of the 100 largest U.S. defined benefit pension plans fell to about 75% at the end of January, down from about 100% a year earlier.

Analysts at Milliman Inc., Seattle, are reporting those figures in their latest pension funding index report.

The funded ratio was down from about 77% at the end of December2008.

The total market value of plan assets has fallen to $923 billion, from $1.2 trillion, over the past year, and the plans now need about $310 billion in additional asset value to make good on their promises to pension plan participants, according to Milliman figures.