OPEN MINDS, The Behavioral Health & Social Service Industry Analyst Industry News The annual survey of 30 cities by the U.S. Conference of Mayors cites substance abuse problems, mental illness, and the shortage of affordable housing as the three leading causes of homelessness. The survey, entitled Summary: A Status Report on Hunger and Homelessness in American Cities, 1998, showed an increase in demand for emergency shelter of II % across the cities surveyed, although more than half of the cities stated that there was no unmet demand for emergency shelter. Additionally . . .