Prognostic factor     Group 1     Group 2
Sex    
 Male 3 5
 Female 5 3
Age band    
 21-30 4 4
 31-40 2 3
 41-50 2 1
Risk factor    
 High 4 5
 Low 4 3
If the 17th subject has factors Male, 31-40, High in Group 1:
Total in group 1, 3+2+4=9.
Total in group 2, 5+3+5=13.
17th subject is registered because 9≤13
Table 1: An example of how the dynamic registration works in a setting of an observational study.