Quality Assurance

Measures to Ensure Quality of the Data

As with many occupational epidemiological studies, information on exposure has to be obtained from the relevant industry. In this case, IARC is obtaining work histories as well as measurements of chrysotile-containing dust and fibre concentrations directly from JSC Uralasbest.

The study′s data entry team has access to all original paper sources detailing workers′ occupational information. Paper records are stored in archives, to which the data entry team has direct access to extract and enter information. Multiple original sources of occupational histories exist; this is important as it enables cross-checking for accuracy and completeness.

The availability of detailed occupational records is one of the strengths of this study. This is important because the records were created prospectively (at the time of employment) and are available for all workers, regardless of where they worked or whether they became sick or died, and thus the same type of information can be collected for all members of the cohort.

Measures to safeguard the integrity of the exposure data include the following:

  • Routine queries of the data are conducted to check for duplicate records or implausible values and to monitor the overall progress of data entry

  • IARC obtains a copy of data being entered by the local study data entry team at regular intervals

  • IARC conducts quality control checks of data entered in the databases against the original paper records through duplicate data entry done by IARC staff for a subset of the data. Thus far, quality control checks have been done for the dust measurement data and the completeness of cohort enumeration. For the dust measurement data, IARC compared a subset of 1990 monthly mean dust concentrations as recorded in the study database with the mean values recorded on original paper records and found 98.9% agreement. Checks of cohort completeness were done by comparing a random sample of 500 records from salary books with the cohort roster; of the 500 individuals selected from salary books, 499 could be matched to the cohort. The overall results suggest that cohort ascertainment is largely complete, and there is no indication that any records have been systematically missed.

JSC Uralasbest does not provide and has no access to the information on the health outcomes ascertained for this study. Rather, this separate set of information will be obtained from the region′s Civil Registry (Vital Statistics) Office and the Migration Bureau and subsequently linked to the exposure information by IARC scientists and local study collaborators.

IARC holds copies of all original data (cohort data; exposure data; outcome data, i.e. follow-up vital status or cause of death data), except for personal identifiers.