Young People's Sexual Behaviour
Indicator 7

Age-mixing in sexual relationships

Additional indicator for generalised epidemics

Definition

The proportion of women aged 15-19 who have had non-marital sex with a man 10 years or more older than themselves in the last 12 months, of all those who have had non-marital sex in the last 12 months

Measurement tools

UNAIDS general population survey; DHS AIDS module

What it measures

One of the principle forces driving the heterosexual spread of HIV is age-mixing. Often, the virus is introduced into a new pool of uninfected young people when people in that age group have sex with people in an age group that is already heavily infected. Most commonly, the younger partners are girls, the older partners men. These types of partnerships are especially good at spreading the virus since, for physiological reasons, there is a high risk of infection per act of sex between a young, uninfected girl and a more mature infected man.

In some countries this pattern of mixing is common enough to have been given a name: the "sugar daddy syndrome". AIDS programmes sometimes try to address it directly from both ends: through IEC campaigns aiming to make sex with younger women socially unacceptable among older men, and through initiatives to increase girls' negotiating power. This indicator measures progress made towards reducing the proportion of young women having non-marital sex with older men.

How to measure it

In a general population survey or a survey of young people, respondents are asked about their three most recent sexual partnerships. The question sequence includes a question about the age of the partner, as well as a question about the relationship between the partner and the respondent.

The indicator is calculated by including in the numerator all women aged 15-19 who report sex with a man who is 10 years or more older than themselves, and to whom they are not married. The denominator is all women aged 15-19 who report sex with any man to whom they are not married.

Strengths and limitations

There are two major limitations to this measure. The first is that people often do not know the exact age of their sex partners. This is more likely to be true for casual partners than for spouses. The second is that it is not clear exactly what age difference constitutes an elevated risk of exposure to HIV.

When uncertain about a partner's age, respondents frequently give numbers that "heap" around round numbers such as 30 or 40. This may well distort the indicator. However, it should be noted that the biases introduced through age heaping or age misreporting are unlikely to change greatly over time, so this may be of little consequence in looking at trends.

This measure will not give an exact picture of patterns of age-mixing, and it will not capture small shifts in the age gap between partners. But the substantial changes in age-mixing that HIV-prevention and life-skills programmes promote will be captured, since women are unlikely to mistake an age-mate for a man many years older than themselves. If women increasingly choose to have sex with their age-mates rather than with older men, or if older men become less likely to seek out substantially younger partners, these changes will be reflected in the indicator, regardless of errors in age reporting.

The indicator is confined to extramarital relationships. Young women may also be placed at higher than average risk of HIV infection if they enter a marriage with a substantially older man. However large age differences between men and women in marriage are both common and socially sanctioned in many societies, and few if any HIV prevention programmes are acting specifically to try to reduce the age gap between marital partners. These partnerships are therefore not included in constructing this indicator.

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