Marriage (Exposure to sexual intercourse)

Index of marriage (Cm)

The index of marriage is intended to express the reduction in fertility caused by women not being sexually active throughout their entire reproductive period. The index is often approximated by the proportion of women aged 15-49 who are married.

 

Cm = {Σ m(a) × g(a)} / Σg(a)

where

  • m(a) = age-specific proportions of currently married (or in sexual union) women
  • g(a) = age-specific marital fertility rates (ASMFR)

 

To estimates Cm we take a weighted average of the age-specific proportions of currently married women, with the weights provided by ASMFR. Strictly speaking, we cannot simply take the proportions of all women who are married since the fertility impact of marriage varies depending on the age-distribution of married women. Married women in the central childbearing years contribute more to the TFR than younger (<20) or older women (40+ years) do.

An alternative approach is to take the ratio of fertility of all women to the fertility of those married.

 

Cm = TFR / TMFR

where

  • TFR    = Total fertility rate
  • TMFR = Total marital fertility rate

 

Because marriage is not a reliable indicator of entry to sexual activity in many countries and more data on sexual activity have become available, this factor has been modified to proportion of women sexually active in the model revised by Stover (see section 10). The data on sexual activities among unmarried and married are available in Demographic and Health Surveys (DHS) and Multiple Indicator Cluster Surveys (MICS).