Alex Schwartz uses this terminology in his introduction to highlight that Deep Housing Subsidy Programs such as Public Housing and Housing Choice Vouchers set the monthly rent as a fraction (typically 30%) of a tenants income. Under these programs, when the tenant’s income changes so does the rent. Shallow Housing Subsidy Programs conversely, like the Low-Income Housing Tax Credit, set rents at a below market rate but don’t peg it to a tenant’s income. The rate is typically higher than what is affordable to very low income households.