Retirement Savings and Household Wealth in 2007
"About half of all workers in the United States participate in an employer-sponsored retirement plan of some kind, a proportion that has remained relatively stable over the past thirty years. Beginning in the early 1980s, however, employers began to move away from traditional pension plans – also known as defined benefit (DB) plans – to defined contribution (DC) plans, like those authorized under section 401(k) of the Internal Revenue Code. Unlike DB plans, which are required by federal law to offer a benefit in the form of a life annuity, DC plans are individual accounts that typically pay the employee a lump sum at retirement. In 2007, approximately 21 million workers in the private sector participated in defined benefit plans, while more than 40
million workers participated in defined contribution plans..."

Retirement Plan Participation and Contributions: Trends from 1998 to 2006
"The U.S. Census Bureau periodically collects information from individuals about their participation in employer-sponsored retirement plans. The most recent such survey was conducted from February through May of 2006. After extensive review and editing by the Census Bureau, the survey data files were released to the public in November 2008. This CRS report presents a summary of the data and a comparison of the results of the 2006 survey with similar surveys that the Census Bureau conducted in 1998 and 2003."