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Median age at first sex

Export Indicator

The age by which one half of young men or young women aged 15-24 have had penetrative sex (median age), of all young people surveyed
What it measures

A major goal in many countries is to delay the age at which young people first have sex and discourage premarital sexual activity because it reduces their potential exposure to HIV. There is also evidence to suggest that a later age at first sex reduces susceptibility to infection per act of sex, at least for women.

Rationale
Numerator
Denominator
Calculation
Method of measurement

This measure is constructed from data on current virginity status among young people, not from retrospective questions about age at first sex. In household or special surveys focusing on young people, respondents are asked whether or not they have ever had penetrative sex. A curve is plotted according to the percent who say they have had sex by each single year of age. The age at which the curve exceeds 50 percent is taken to be the median age at first sex. On average, people reporting they are a certain age will be six months older than that age. (For example those who say they are 15 will range from those who turned 15 on the day of the survey to those who will turn 16 the following day. Assuming an even age distribution, they will be on average 15.5.) Half a year should therefore be added to the exact ages used in the calculation of the median age at first sex.

Measurement frequency

Every 4-5 years

Disaggregation

Condom type: N/A

Education: N/A

Gender: Male, Female

Geographic location: N/A

HIV status: N/A

Pregnancy status: N/A

Sector: N/A

Service Type: N/A

Target: N/A

Time period: N/A

Type of orphan: N/A

Vulnerability status: N/A

Explanation of the numerator
Explanation of the denominator
Strengths and weaknesses

Because this indicator is constructed from a question about current virginity status, it is sensitive to recent changes in the age at first sex. The indicator itself does not, however, give any idea of the full distribution of ages at sexual initiation. In some circumstances, such as when a significant proportion of girls is exposed to sex at very young ages, it may be the tails rather than the middle of the age curve which interest those designing prevention programmes. To allow for the construction of a robust indicator using this “current status” methodology, reasonable sample sizes are needed at each single year of age (preferably at least 100 respondents of each sex in single years, especially the single years at which the median age is expected). Most questionnaires also include questions such as “How old were you when you first had sex?”. These data are not used in the construction of this indicator. This is because they exclude people who have not yet had sex, and therefore tend to bias the median age downwards. Retrospective data can be used from age cohorts at which virtually everyone is already sexually active. However an indicator constructed in this way is not sensitive to recent changes in the age at first sex, and it is these recent trends that are of interest in monitoring the success of HIV prevention programmes. The indicator is most useful where the median is rather young – between 15 and 19 years. Where the median age at first sex is over 19 for both men and women, promoting abstinence among adolescents may be replaced by other priority interventions within the programme and this indicator will diminish in importance and may not even be measured.

Further information