Table 1. The effectiveness of mammographic screening on breast cancer mortality expressed by odds ratios, according to calendar period of index-invitation at screening and corrected for age at invitation.

Calendar period of index-invitation	Cases screened (unscreened)	Referents screened (unscreened)	Odds ratio (95% CI)
1975–2008	191 (91)	1089 (321)	0.65 (0.49–0.87)
1975–1991	90 (40)	501 (149)	0.72 (0.47–1.09)
1992–2008	29 (23)	202 (58)	0.35 (0.19–0.64)

Abbreviation: CI=confidence interval.