Contraception
The index is intended to measure the fertility-inhibiting effects of contraceptive use. The index is calculated as below.
Cc = 1-1.08 × u × e
where
- u = prevalence of current contraceptive use among married women of reproductive age
- e = average use-effectiveness of contraception
Here, the index of contraception varies inversely with prevalence and use effectiveness of contraception. If contraceptive practice is absent of completely inefficient, Cc=1.0.
The factor 1.08 represents an adjustment for the fact that couples do not use contraception if they know or believe that they are infecund. The absence of contraception among such infecund couples implies that the contraception that is practise is concentrated among fertile couples. Therefore, u, which measures prevalence among all couples, has to be inflated to take account of this concentration of contraception.