Imputation of missing technology classification in worldwide patent data

The file tech_all.txt contains identifiers for patent first filings (corresponding to appln_id in PATSTAT), technology fields and technology sectors from PATSTAT table TLS230_APPLN_TECHN_FIELD. The file ipc_all.txt contains identifiers for patent first filings (corresponding to appln_id in PATSTAT) and International Patent Classification (IPC) from PATSTAT table TLS209_APPLN_IPC. The file cpc_all.txt contains identifiers for patent first filings (corresponding to appln_id in PATSTAT) and Cooperative Patent Classification (CPC) from PATSTAT table TLS224_APPLN_CPC. Missing information has been imputed from equivalents and other second filings. The files also contain a variable indicating the source of information ('source'): The field 'source' indicates where the information on technology classification comes from : 1 = information available from the patent itself, 2 = information availabe from the earliest direct equivalent, 3 = information available from the earliest subsequent filing. It is possible to select certain types of first filings based on column 'type'. For example, Paris Convention priority filings can be retrieved by specifying type='priority'.