There are three issues that need to be addressed in order to begin to answer this question.
- What is the definition used by the Council of Europe (CoE), in determining whether a child is a victim of sexual violence?
- Is "child victim of sexual violence" synonymous with criminal sexual abuse of children, i.e. is consensual sexual activity between two 16 year old's counted as a form of sexual violence and abuse if the legal age of adulthood is 18?
- Is the prevalence of such abuse stationary over time, especially as demographics in Europe have changed? Specifically, the most recent study referenced by the CoE website was published in 2010 and others dated back to 2003.
The summary-level definition of childhood sexual violence provided by the CoE is the following (via Is it really ONE in FIVE?):
sexual abuse, pedopornography, solicitation of children through
Internet, child prostitution and corruption of children
That definition could be considered somewhat vague, especially corruption of children. The CoE provides a much more precise definition, which addresses both issues 1 and 2 above, in the Council of Europe Convention on the Protection of Children against Sexual Exploitation and Sexual Abuse (2007), see Article 3 – Definitions:
“sexual exploitation and sexual abuse of children” shall include the
behaviour as referred to in Articles 18 to 23 of this Convention [and]
“victim” shall mean any child subject to sexual exploitation or sexual
Articles 18 to 23 are very specific. Part 3 of Article 18 explicitly states that consensual sexual activities between minors is not sexual abuse, thus resolving potential false positive data for the situation in issue 2 (note that "Party" refers to each European nation state that is a signatory):
Article 18 – Sexual abuse
Each Party shall take the necessary legislative or other measures to ensure that the following intentional conduct is criminalised:
(a) engaging in sexual activities with a child who, according to the
relevant provisions of national law, has not reached the legal age for
sexual activities; (b) engaging in sexual activities with a child
- use is made of coercion, force or threats; or
- abuse is made of a recognised position of trust, authority or influence over the child, including within the family; or
- abuse is made of a particularly vulnerable situation of the child, notably because of a mental or physical disability or a situation of dependence.
For the purpose of paragraph 1 above, each Party shall decide the age below which it is prohibited to engage in sexual activities with a
The provisions of paragraph 1(a) are not intended to govern consensual sexual activities between minors.
Article 22 provides clarity on "Corruption of children" which is definitely a form of sexual abuse and not merely something subjective such as changing an infant's diaper in public:
Each Party shall take the necessary legislative or other measures to
criminalise the intentional causing, for sexual purposes, of a child
who has not reached the age set in application of Article 18,
paragraph 2, to witness sexual abuse or sexual activities, even
without having to participate.
The remaining Articles cover everything else: child prostitution, child pornography, participation of a child in pornographic performances, and solicitation of children for sexual purposes (e.g. through the Internet, SMS and so forth).
Issue 3 mentioned above is relevant due to recently changing demographics (especially due to migration to Europe as a result of EU policy changes from 2015 onward) and the impact on attitudes about consent, including children. It is a moot point though, if we cannot establish whether the "one in five" statistic was an evidence-based finding as of 2007-2010. In other words, we can't determine if the prevalence is increasing over time without a benchmark to confirm that 1 in 5 is accurate, an under-estimate, or an (unlikely but possible) over-estimate.
Based on this document, 1 in 5 Fact Argumentation [PDF] published by CoE, it appears that the "one in five" statistic was intended as a starting point, to begin collecting data, rather than as a final result, emphasis mine:
Most available research refers only to sexual abuse involving physical
contact, so the figure ONE in FIVE may actually be underestimated,
given the increase in solicitation and exposure of children to
pornographic material through the Internet. Not knowing the real
extent of sexual violence due to a lack of reliable data has resulted
in poor prevention strategies.
Because most people underestimate the extent of the problem, the Council of Europe ONE in FIVE campaign
uses an estimate as an effective base-line study tool to motivate
governments, parliaments, child professionals and parents to take the
urgent action needed to prevent sexual violence, protect children and
The most authoritative study cited by the CoE website, Overview of the Nature and Extent of Child Sexual Abuse in Europe (2010) (full text, uploaded by the authors, Kevin Lalor & Rosaleen McElvaney) reported prevalence rates of child sexual abuse with very wide variation bands, and significant differences by gender and by European country.
Lampe (2002) reviewed 24 European studies conducted in Germany,
Switzerland, Great Britain, France, Sweden, Austria, Belgium, Denmark,
Finland, the Netherlands and Spain found overall prevalence rates of
6% to 36% in girls and 1% to 15% in boys under the age of 16.
May-Chahal and Herczog (2003) examined a number of European prevalence
studies and reported rates of rape were 0.9% for females and 0.6% for
males. When broader deﬁnitions of child sexual abuse are used, the
rates were 50% for females and 25% for males.
The conclusions are as follows:
There is no co-ordinated centralised measure of the incidence of child
sexual abuse in Europe comparable to the US National Incidence Study
of Child Abuse and Neglect (NIS)... Instead, independent research
studies using a range of deﬁnitions and methodologies exist. These
vary in size and sophistication. However, even the most comprehensive,
using national probability samples, are generally “one-off” and
provide only “a snapshot in time”. They are rarely repeated using
methodologies that would allow comparisons across time, so we have
very little data on trends in child abuse.
It is impossible to know the true incidence or prevalence
of child sexual abuse in Europe...
This makes it very difficult to validate the 1 in 5 data point.