NOTE ON THE TIME SERIES CONTRACT DATA
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++ There are two time series files: "time_series_naics2.csv" and "time_series_states.csv."

++ In each file, contract obligations are aggregated in the month in which the transaction occurred (the month of the "action_date" variable that
   can be found in the base files.
   
++ Each file has a "total_obligations" variable, which represents the sum of "federal_action_obligation" in a given month x state or month x sector.

NOTES SPECIFIC TO THE SECTOR FILE:
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++ NAICS 2 codes are constructed as the first two digits of the "naics_code" variable in the base files.

++ Observations in which a naics_code was not reported have been dropped. 



NOTES SPECIFIC TO THE STATE FILE:
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++ States represent the "primary_place_of_performance" of a contract transaction.

++ In the raw USASpending data, the variable "primary_place_of_performance_state_fips_code" is called "prime_award_transaction_place_of_performance_state_fips_code." The name has been changed here for brevity, but the variable is the same. 

++ Observations in which the state was not reported are dropped.