Record-Linkage of Other Databases

RECORD-LINKAGE OF OTHER DATABASES

Most of primary and secondary care use the CHI number as the patient identifier; however, if data do not have CHI numbers, these can be allocated from patient demographic details, such as name, date of birth and postcode. MEMO can identify the correct CHI number for a very high proportion of patients in the database. This is the same method as is employed to allocate CHI numbers to prescription data. MEMO has constructed a database of 100 000 endoscopy and colonoscopy procedures, and, in collaboration with Tayside Police, subjects involved in 22 000 road traffic accidents in Tayside using this allocation procedure.

CLINICAL LABORATORY DATA

Clinical laboratory investigations for the Tayside region since 1989 are held on a computerised archive in the Department of Biochemical Medicine in Ninewells Hospital. The database has CHI-specific biochemical, haematology, microbiology, virology and serology laboratory results and reports. CHI-specific results from all pathology investigations since 1990 for Tayside are electronically stored in MEMO. These data can be record-linked to the MEMO database to complete the clinical characteristics of disease or hospital admission.

PRIMARY CARE DATA

Progressively more GPs are using computerised systems to aid in patient management, although at present they are not available to MEMO for record-linkage. However, it is possible to abstract writ-ten records in primary care manually and research nurses in MEMO have been granted access to primary care records for specific studies (Morris et al., 1997a; Evans et al., 1998).

OTHER INFORMATION

Since all patients and their addresses are known, including postcode, and information is available from the decennial census regarding the relative deprivation levels of postcode areas, the so-called Carstairs depri-vation score can be used as a relatively crude indica-tor of the socioeconomic status of patients (Carstairs, 1990; Evans et al., 1997a). The deprivation category component variables are the percentage of people in a postcode sector with no car, the percentage living in overcrowded housing, the percentage with the house-hold head in semi- or unskilled occupations, and the percentage of men unemployed.

Details of all deaths in Tayside since 1989 are elec-tronically recorded through a copy of the General Registers Office – Death Certification Database and held within MEMO. The date and underlying cause of death can be identified and linked to the MEMO database using the CHI number of the patient.