Case-control study Finland (Nieminen, Int J Cancer, 1999)
 | History of previous Pap smears in 156 cancer cases, 1139 controls
| OR for no screening (ref)= 1
| OR if organised screening: 0.25 (.13-.48)
| OR if opport. screening: 0.57 (.30-1.06)
| OR if org. & opp. screening: 0.27 (.15-.49) | |