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Table 1 Selected characteristics of mammographic screening programs

From: Mammographic features associated with interval breast cancers in screening programs

Program National Breast Screening Study (NBSS) British Columbia (SMPBC) Ontario (OBSP)
Years of operation 1984-90 1988-present 1992-present
Incident cancers selected for present study in years 1984-90 1993-99 1993-98
Number of first examinations in selected years 45,000 250,584 166,254
Recruitment Self-referral Letter of invitation, physician and self-referral Physician and self-referral
Number of centers 15 19 8
Ages 40-59 40-70 50-69
Frequency of screening Annual Annual Every 2 years
Physical examination Yes No Yes