For most Americans life without a home is almost beyond imagining. What you have, essentially, is what you can carry. Among the things you don't have, essentially, are windows, floors, doors, walls, furniture, a stove, a refrigerator, a closet, any place to go to and any privacy. What does living like that do to you? And what if you have kids, as an estimated 20 percent of America's two to three million homeless have—what does it do to them?

Dr. Ellen Bassuk, associate professor of psychiatry at the Harvard Medical School, is one of the few people who has tried to find out. While running the emergency psychiatric service at Boston's Beth Israel Hospital in the '70s, Bassuk saw firsthand that many of the homeless were ex-mental patients discharged from hospitals to live in community mental health centers—most of which had somehow never been built. In 1982 Bassuk devoted herself to studying and interviewing hundreds of the homeless and especially the mentally ill and mothers with children, who together form the bulk of the homeless population. The work has made her a pioneer in a field conspicuously lacking in either scientific analysis or solutions. This March, Bassuk, 40, will help lead a national conference in Boston on homelessness. At the comfortable suburban Brookline, Mass. home she shares with her husband, Dr. Stephen Schoonover, Bassuk shared her insights on the psychology of the homeless with Jon Keller.

How does homelessness affect people's minds and emotions?

All homeless people are depressed and anxious. Being homeless erodes people's self-esteem. It makes them invisible, without any real identity. It strips them of the normal things most of us take for granted and reduces them to another level of existence, a grotesque existence. Every day the homeless need to find a way to put food in their bellies or survive in the cold. They are regularly assaulted; the women are regularly raped. So their depression is at a much more profound level than most people's. They don't have the usual connectedness to other people and to caretaking institutions. They're isolated and estranged. What everybody should imagine is what it would be like to lose absolutely everything, so that you don't even have somebody to call up.

How many homeless are mentally ill?

In the adult male and female population, the figure the American Psychiatric Association estimated is between 25 and 50 percent, mainly people with psychotic disorders. Some alcoholics could also be considered chronically mentally ill. These chronic mentally ill may act bizarre, gesture, talk to themselves, be disheveled or talk in a "word salad." In the homeless family population, however, it's much more complicated. We found that many homeless mothers suffered from depression and emotional problems, which affected their ability to cope. But they were not former mental patients, and they did not have psychoses.

Why are so many of the homeless chronically mentally ill?

Some people suffer from psychotic depressions and manic depressive illness, but schizophrenia is most common and can limit a person's capacity to function. Generally not more than 10 to 15 percent of schizophrenics can live independently. Those on the street usually don't have families. With deinstitutionalization and the destruction of single-room-occupancy hotels in most cities, there is no place for these folks to go. Despite all the deprivation and horrors in institutions, at least they housed people.

Do people become mentally ill as a result of being homeless?

It's my impression that very few do. In our two studies, we found that mental disorders began before a person became homeless. However, if anyone has been traumatized by homelessness, obviously it can leave lasting scars.

Do many homeless men and women commit suicide?

The vast majority are not suicidal, but the reasons for that are not clear to me. Sometimes you wonder whether homeless people have enough energy to plan a suicide. There are complex reasons why people struggle to stay alive, and for most groups we have little to go on, but we can speculate that parents with children don't want to abandon them. One hundred percent of the mothers we interviewed spoke about how important their kids are to them. These mothers love their children.

How does homelessness affect young children?

What we found was depressing and devastating. Close to half of the kids 5 years and younger had at least some impairment in major developmental areas. A lot of the other little kids were not responsive; they were listless and depressed. When you pick up children, they generally mold into your arms. But some of these kids did not. Mothers would tell us that when they brought their kids to shelters, they would stop eating and wake up in the middle of the night. The children would tell us how awful it was to be there and how scary the shelters were.

Is homelessness harder for children than for adults?

It's much tougher for a child. During their first five years of life, children need to learn emotional and social skills from their environment. They need stability and nurturance from their caretakers, but their mothers are often so distressed they really can't provide it.

How do older children adapt?

School-age kids are embarrassed about being homeless. They won't tell their friends. They figure out circuitous ways of getting back to the motel or shelter so nobody knows. A third of the older children we interviewed had evidence of clinical depression, which is a very high percentage; almost all said they had suicidal thoughts. Approximately 43 percent had repeated a grade at school, and almost half were below average or failing. One mother told us that her 10-year-old boy was very anxious. We asked how she knew. "Well," she said, "he pulled out several of his permanent teeth." All these kids are very sad, despairing, depressed and puzzled. But there's nothing really inherently wrong with any of them. They just need to have a stable living environment.

Are there family factors that predict homelessness?

In looking at the histories of the mothers, we found that some who were most chronically homeless came from homes where there had been early disruptions, where they had lost both parents and even ended up in an institution or with a relative. Others had been abused and neglected by their own mothers. Now they have histories of abusing and neglecting their own children, even if they love them very much. In the five years prior to becoming homeless, most of the mothers we interviewed had led lives of chronic disruption. Some of their preschoolers had already moved four to six times.

Do homeless mothers share any other traits?

There aren't any common outward expressions. Many are articulate, animated and seemingly well adjusted. But the vast majority were sheltered in areas where they grew up—so that they have long ties to the community—yet they were not able to name anybody with whom they had a relationship. They had terrible trouble forming and maintaining relations with men, or even with women. Some of them named their child, sometimes a preschooler, as their main support in life. Or the only person they could name was a recent shelter friend. Many of these mothers also have poor or nonexistent work histories; more than half had been on welfare for a fairly long period, two to four years or more.

What is the main reason people are homeless? Is it the discharge of the mentally ill from institutions? The lack of housing?

It's not purely psychological or purely economic. When the bottom of society falls out, it stands to reason that the most marginal person falls out first. The combination of deinstitutionalization and the collapse of the housing market combined to make the mentally ill a very vulnerable group. The so-called safety net of institutional supports has developed a lot of holes in it, so we're seeing all kinds of people falling out now. If the bottom falls out deeply enough, it's going to start affecting better and better functioning people.