Information on dates of invitation, attendance, breast cancer diagnosis, emigration, death, and cause of death was linked by using unique 11-digit personal identification numbers assigned all inhabitants of Norway at birth or immigration.
From the screening database we further retrieved data on tumour grade (based on the Nottingham grading system, I-III 22); oestrogen and progesterone receptor status 21; pTNM classification; and dates of invitation and attendance to the screening programme.
We received an anonymized file with individual level dates of invitations and attendance for all women who were invited to the NBCSP and linked this information to the dates of diagnosis of breast cancer, emigration, and death (Fig. 1).
The screening histories of all women in the cohort, including the dates of invitations and the dates of all their screening tests following the invitations, if any, were extracted from the local computerized screening database.
date of birth, date of diagnosis (if a case), stage at diagnosis (if a case), date of death (if a case), and complete screening history including dates of invitations and attendances, and outcomes of attendances.
The following information was obtained: date of birth, date of diagnosis (if a case), stage at diagnosis (if a case), date of death (if a case), and complete screening history including dates of invitations and attendances, and outcomes of attendances.
The programme in Funen started on 1 November 1993 and invited women aged 50-69 athehe date of invitation.
To qualify, a candidate must have on the date of invitation the support of an average of at least 15percentt of those polled in five national surveys.
7 The exact date of invitation was not available in the screening register.
Data from the booking system (civil registration number, screening round, date of invitation, date of screening, and date of sending the screening result to the woman) in each of the five Danish regions are transferred electronically to the DKMS.
Usually age is the only risk factor measured when evaluating population-based breast cancer screening programmes, because information on date of birth and date of invitation of women is mostly available.
