CHESTNUT HILL, Mass. I've come to Boston College and the Center for Retirement Research to visit Alicia H. Munnell. I'm here because the former assistant secretary of the Treasury for Economic Policy is a kind of mapmaker.

No, she doesn't draw the mountains and valleys of geography.   Ms. Munnell is the economist you visit when you're looking for the 'map' of an economic issue, a map that isn't bent to the political predispositions of a think tank or public policy institution.

My question is simple: what are the most important features on Americas' retirement income 'map'?  

If you listen to her answer you'll probably remember an old proverb. Just as the man who had no shoes felt sorry for himself--- until he met a man who had no feet--- today's 401(k) participants would feel fortunate if they met the multitudes that have no retirement plan of any kind.

"Half the population is covered by one type of pension or another. It may be DB (defined benefit) or DC (defined contribution), but the figure doesn't change much. It also doesn't matter how you slice the pie--- whether you look at full time or full time and part time workers, etc.--- it's about half.

"When we start to talk about people who are unhappy with their 401(k) plan it's important to remember: they are a privileged population. Other workers--- about half--- have no coverage."

  That blunt reality, she points out, is often obscured by our attention to events affecting those who are covered such as the decline of conventional pension plans and the rise of defined contribution plans.

"Of households with pension coverage, 60 percent have only DC plans, 20 percent have DB plans, and 20 percent have both," she notes.

"The decisions confronting most workers are familiar. First, whether to join the plan? Second, if you join, how much to contribute? Third, how do you invest the contributions?

"There, my coworker Annika Sunden has found an enormous amount of inertia. Worse, the number of choices keeps growing. Fidelity (Investments) now brags that their larger plans average 30 choices. That's ridiculous."

I asked why.

Professor Munnell answered with a story about choosing jams. "A company did some research in customer choice. One day they put out 26 different types of jams. You could sample them. If you bought one, you got a dollar off. People circled the table and talked a lot. But they didn't buy.

"On the next weekend they put out only six types of jam. People gathered around the table, sampled, and bought jam."

For Ms. Munnell, however, such fine lines on the "covered" portion of the map disappear before a single over-riding reality: half of all households have no pension coverage beyond Social Security.   Social Security, meanwhile, is replacing less income for retirees.

I asked her to explain.

"It's the retirement age." Taking a page from a presentation she had made in Iceland only a few days earlier, she pointed to 1990. Then, Social Security benefits could be expected, on average, to replace 43.2 percent of pre-retirement income. By 2010 the figure was expected to fall to 39.5 percent. By 2030 it would hit 36.7 percent.

Whatever the issues for people who are covered, they paled against the problem faced by people with no private pension plan and diminishing Social Security benefits. The reason, she explained, is that full retirement benefits are only received if you retire at full retirement age. Social Security, however, is slowly raising the age of full retirement from 65 to 67. Since most workers retire before age 65, this amounts to a de-facto cut in benefits.

Is there a solution?

Her answer was tentative. "I don't think a voluntary, employer sponsored plan is the answer. I'm not sure low income people can afford to give up income for future benefits… The only answer may be to keep people working."

Stay tuned.