Information on clinical characteristics is gathered from linkage with the Netherlands Cancer Registry and with hospital databases.
Women with screen-detected cancers were identified from linkage with the breast screening centres that serve the population base.
In total, we identified 922 Michigan born offspring to 496 PBB cohort mothers from linkage with electronic birth records.
Information on mortality/survival is gathered from linkage with the Municipal Personal Records Database (in Dutch: Basisregistratie personen), information on cause of death is ascertained by linkage with Statistics Netherlands.
Breast cancer cases were identified in each cohort by self-report with subsequent confirmation of the diagnosis from medical records or tumour registries and/or from linkage with population-based tumour registries (method of confirmation varied by cohort).
Baseline factors associated with self-report and subsequent behavioural, utilisation and clinical differences between those who did and did not self-report were defined from the survey responses and from linkage with administrative data sources.
Complete follow-up of all patients is crucial to avoid selection bias, which can easily arise if information on SMNs is not derived from linkage with nationwide cancer registries, but from patient questionnaires or medical records.
The linked NBSS data was used directly to replace the ethnic group of cases not already known from linkage with HES, rather than as a separate predictor in the imputation model.
Of the 946 women in the final model, data on breast cancer status was obtained on 712 (75%) by completed questionnaire data and on 238 (25%) from linkage with the CCR database.
