This table shows the types of links that are supported by the CRSP CCM link and how they are achieved. A date range is associated with each link so all actions imply an event history.
|1||Find all securities in CRSP for Compustat Company data||GVKEY||PERMNO (PERMCO)||crsp_ccm_link (all links used)|
|2||Find primary security in CRSP for Compustat Company data||GVKEY||PERMNO||crsp_ccm_link (only links where LINKPRIM is P or C)|
|3||Find data in CRSP for a specific Compustat Company and issue||GVKEY/IID||PERMNO||crsp_ccm_link (links with desired IID)|
|4||Find Compustat data for a given CRSP security.||PERMNO||GVKEY/IID||crsp_ccm_linkused (history used to build a composite GVKEY record in link used)|
|5||Find Compustat company and security data for a CRSP security, only if it is considered primary.||PERMNO||GVKEY/IID||crsp_ccm_linkused (only use links where LINKPRIM is P or C)|
Link Action Notes:
- CRSP_CCM_LINK contains valid links for all securities provided by Compustat. Each record with a valid link to a PERMNO can be followed to the appropriate CRSP data. The user has the option of restricting links by LINKTYPE to ignore soft links, and using the CRSP PERMCO to identify other issues of the same company not addressed in the link. All PERMNOs found with this method share the company-level data from the GVKEY. The link record IID is needed to match the CRSP PERMNO data to the proper Compustat security level data.
- Link records with the security not marked Primary are ignored. Otherwise this is the same as #1. The result is that even if multiple CRSP PERMNOs are found, there should be no overlap in the CRSP history used. All PERMNOs found will share the company-level data from the GVKEY, but will match only the Compustat IID indicated in the link record.
- Given a GVKEY and IID from Compustat, use CRSP_CCM_LINK to get the history of CRSP PERMNOs linked to that company and security. The user has the option of restricting soft links using LINKTYPE. No consideration is given to whether the security is considered primary any time during its history. The link can produce multiple CRSP PERMNOs, but only one link should be found at any time.
- Given a CRSP PERMNO, use CRSP_CCM_LINKUSED to find Compustat data. Access with APERMNO key type will build a composite GVKEY record from the used link records. CRSP_CCM_LINKRNG is used to find ranges of data for the composite record. Secondary links are ignored, and only the Compustat security data matching the permno are included. There will be one composite security record created with a pseudo IID of 01X.
- Same as #4, but a link record is ignored if the security matched is not primary. This will result in a smaller range, and a not-found if the PERMNO is never primary for the company. Access with PPERMNO key type is used to select this method.
- PERMCO is not directly supported with linkused, but attached PERMNOs can be found from the PERMCO and the user can select securities with PERMNO. To avoid double-counting company data, the primary flag can be used to ensure that only one security is represented during each time range.
4, 5 A user can use secondary index on PERMNO or PERMCO to find GVKEYs with matching information and see the Compustat data in native form, then handle processing as desired. These reads are not necessarily unique, so it is left to the user to select information from the correct ranges corresponding to the desired CRSP identifier.