The trauma of having no home imposes unique health problems on families, especially children. Homeless children are more subject to infectious diseases, are more in need of immunizations, and have more growth and developmental problems than children growing up in nurturing environments. A study of the homeless in St. Louis found that increasingly they are families headed by single women who had to leave their homes mainly because of overcrowding. A study of data obtained from healthcare clinics set up at shelters showed that the mean age of homeless children was 4.9 years; the mean number of months they had lacked a permanent residence was more than four. Healthcare screenings showed that chronic health problems, such as asthma and anemia and deficits in growth and development, were among the top 10 diagnoses. Less serious problems like colds and lice were more prevalent, however. Intelligence tests administered to homeless children showed that they had three times the cognitive and developmental problems that would be expected among children in general.