“Young people are having sex for the first time at younger and younger ages.” “The average age at which American (British, Swedish,
Australian…) adolescents begin sexual activity is 15 (16, 17…).” “HIV/AIDS
education needs to take place at
correspondingly young ages..”

How many times do we read statements like this in news
stories and studies? And how informative are they, really? A letter published online in the Archives of
Sexual Behaviour recently suggests that references to “average age” or “mean
age” in studies about adolescent sexual behaviour can be quite misleading.

In a study of adolescents in Europe, for example, one reads
that “compared with previous generations, young people (16–20 year-olds) were
having intercourse for the first time at an earlier age, on average at 16.5
years of age”. (Avery & Lazdane, 2008)
A superficial reading could suggest that “most young people” are sexually
active at that age, although the statement does not, in fact, tell us how many
are sexually active.

It seems that researchers focussed on epidemics of HIV/AIDS
and STIs are so keen to catch adolescents before they have any risk of
contracting these diseases that they are at risk themselves of creating false
impressions. And, one might add, pushing back the age for sex education into
early childhood.

Jokin de Irala and colleagues at the University
of Navarra, Spain, say in their letter that it
is time to clear up the confusion generated not only amongst journalists but
even amongst public health policy makers and health education managers -- not
to mention young people themselves.

The task is not difficult; it requires that researchers
report the proportion of the age
group which is sexually initiated, not just the average age at which that
occurred. When that is done, the big picture looks very different. De Irala and
colleagues are doing an international study of high school students -- Project YOURLIFE
-- that illustrates the point.

In what appears to be a ground-breaking study, they used
data from questionnaires answered by 7011 students in El Salvador, Peru and
Spain, and compared the actual percentages of young people who were sexually
active at different ages with mean and median ages.

The researchers found that in each of the three sites, the
majority of young people whose ages were close to any of the three measures of
“mean age of first sexual intercourse” were not sexually active. For example, mean ages of first sex in El Salvador, Peru and
Spain were 15, 14 and 16 years respectively whereas the proportion of youth
from ages close to those means that were sexually active was 21 per cent, 9.6
per cent and 22 per cent respectively. (See table published with the letter.)

The authors of the letter comment:

“The extensive use of mean age of sexual initiation in the
scientific literature and consequently in the media suggests that the potential
for misleading interpretations is not being adequately taken into account.
Studies that use mean age of sexual initiation usually use age ranges that do
not take into account those who have first sex at older ages or who never have
had sex at all. This essentially biases the interpretation of such means.”

In conclusion they point out that greater precision in
communicating facts about adolescent sex “can be of crucial help to health
policy makers and health education managers who are trying to convey the
importance of delaying sexual initiation among youth.

“We therefore encourage the use of the percentage of youth,
at different ages, who have already initiated sexual relationships instead of
the use of averages. This will reduce confusion, help avoid erroneous
interpretations, and provide a much needed additional source of support to
young people, all of which in time gives such public health policies a better
chance of succeeding.”

Amen to that.