Changes from dataset version 2 to version 3:

Added common-control name fields cc-a (common control name, augmented with study area name where common control name is blank), cc-as (cc-a, with names standardized), and cc-asc (cc-as, with control names corrected).  There's remains considerable room for improving the correctness of cc-asc.

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Changes from dataset version 1 to version 2:

Added calculated totals for plant-specific expenses (DL445) and corporate operations expenses (DL565)
Imputed missing values for Tier, 1988-1991 from values for 1992-3
Imputed missing values for Regulatory Type, 1989, from values in 1990
Imputed missing values for State, 1988-91, from values 1992-2007
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Version 1 notes:

Note: year specified below are filing years (data year= filing year -1)

1989: added YEAR,coded from PRD (1989)
1989:  renamed fields for consistency with t90-97, including fields D and T to F and CALC, respectively

1989: 14 records with null study-area name, study-area code doesn't match to any record 1989-2009 with non-null study-area name

1989-1993, 1996: no common-control codes (but common-control names)

1990: 3 records with null study-area name, study-area code doesn't match to any record 1989-2009 with non-null study-area name; these records also have null regulatory type field

1990-97: created year field from PRD, deleted PRD (which contained year followed by "1")

1990-97: consolidated CC_ABBR into CC_NAME

1990-97: renamed non-accounting fields to corresponding t98-09 fields where existed

1990-97: deleted F variable: contained "L" for all fields in all years, except 1991 and 1992, for which it was null

1990-92: where applicable, common-control name field explicitly declared "NO COMMON CONTROL"; changed to null

1998:  DL265_3100_2200 transferred to DL265_3100_2220

1998: DL480_6620_TOTAL, DL485_6620_BENEFITS transferred to DL475_6620_TOTAL, DL480_6620_BENEFITS, respectively

1998: 20 records with null study-area name (contained only non-printing characters) updated by matching study-area code to 1997 record and populated from that record saname, ccname,cc_code, state,subset, and tier

1999: DL370_6120_BENEFITS, DL375_6120_RENTS transferred to corresponding 6120 field

1999: DL395_6320_TOTAL, DL400_6320_BENEFITS, DL405_6320_RENTS transferred to corresponding 6230 field

1999-2000: DL545_6720_TOTAL, DL550_6720_BENEFITS duplicate DL550_6720_TOTAL, DL555_6720_BENEFITS; former deleted (null elsewhere)

1998-2009: deleted variable DAS (1 for all records)

1989-2009: state standardized to postal codes

1998: field RURAL coded as N/A for all records, changed to null

1999: field RURAL coded as Y for all records, changed to null

1990: regulatory type not coded

study area names not standardized

common-control names not standardized

common-control codes occasionally differ for records with same common-control name