Is the “Metropolitan area FIPS code” consistent throughout the years? Can I merge data to metropolitan level using “metfips”?

Definitions of metropolitan areas as well as METFIPS codes change over time. Prior to 1977, the code scheme used is CPS-specific. After 1977, the code scheme is the metropolitan area’s FIPS code. Starting May 2004, New England metropolitan areas are defined using New England City and Town Area (NECTA) definitions. The codes for these areas correspond to NECTA codes, not to the metropolitan area (CBSA) FIPS code. So, the ability to simply merge data using METFIPS ultimately depends what time periods you are analyzing. See under the Codes tab for more details on the specific codes over time.