Countries where very few young people have sex before the age of 15 might opt to use an alternative
indicator: percentage of young women and men aged 20–24 who report their age at sexual initiation as
under 18 years. The advantage of using the reported age at which young people first had sexual intercourse (as opposed to the median age) is that the calculation is simple and allows easy comparison over time. The denominator is easily defined because all members of the survey sample contribute to this measure.
It is difficult to monitor change in this indicator over a short period because only individuals entering
the group, i.e. those aged under 15 at the beginning of the period for which the trends are to be assessed, can influence the numerator. If the indicator is assessed every two to three years, it may be better to focus on changes in the levels for the 15–17 age group. If it is assessed every five years, the possibility exists of looking at the 15–19 age group.
In countries where HIV-prevention programmes encourage virginity or delaying of first sex, young
people’s responses to survey questions on this issue may be biased, including a deliberate misreporting of age at which they first had sex.