| Variable | Definition | Source |
| Endogenous variables | ||
| GPOP | Growth in population density by county | EBA |
| GEMP | Growth in employment density by county | EBA |
| GPCI | Growth in per capita income by county | C&CDB |
| GRE | Growth in number of retail establishments (density) by county | SUSB |
| Initial conditions | ||
| POPBASE | County population density in 2000 | USCB |
| EMPBASE | County employment density in 2000 | EBA |
| PCIBASE | County per capita income in 2000 | C&CDB |
| REBASE | County retail establishment density in 2000 | USBS |
| Accessibility variables | ||
| METRO
| Metropolitan counties, dummy variable = 1, 0 otherwise | ERS |
| METROADJ | Counties adjacent to metro areas, dummy variable 0, 1 otherwise | ERS |
| ROADDEN | Interstate road density | NRAC |
| Economic variables | ||
| NFIRMS | Density of number of firms by county | USBS |
| PCITAX | Per capita income tax | C&CDB |
| PTAX | Property tax on business | USCB |
| POVERTY | Percent of families below poverty line | USCB |
| CMHV | County’s median housing value | C&CDB |
| EGOV | Per capita government expenditure | C&CDB |
| PHP | Density of housing permits | C&CDB |
| CBSI | Density of banking and saving institutions | C&CDB |
| Socio-demographic variables | ||
| RETIRE | Percent of population above 65 | C&CDB |
| NONWTE | Percent non-white population | C&CDB |
| OPERATIVE | Percentage of population between 16 and 64 | C&CDB |
| COLLD | Percentage of population 25 years and older with college degree | C&CDB |
| CRIME | Serious crime rate (felony, violent crimes, etc.) | C&CD |