MODULE 1: SEX OFFENSES, OFFENDERS AND VICTIMS
Onset of Sex Offending
The presentation now focuses on the article by Lussier and Mathesius, titled "Criminal Achievement,
Criminal Career Initiation, and Detecting Avoidance, the Onset of Successful Sex Offending." The age
of onset and detection avoidance of sex offending were seen as a central point of this investigation.
It has been shown to be informative of certain aspects of criminal behaviors and careers, including
career length, continuity, persistence, specialization, seriousness, and frequency. Nagin et al, in
1995, stated the imperfect but significant association between onset and offending frequency has
led criminologists to gradually shift their attention to the examination of offending trajectories, in
which onset, offending rate, and changes in offending rate over time are analyzed simultaneously.
Onset has been examined in two ways. The first has been the approach by developmentalists to
look at earlier development of onset and life course development, as well as predictable pathways
of offending and changes over time. The second approach is that of the life course theorists, which
suggest that the relationship between onset, in the course of lifelong criminality, lacks relevance as
it is to imperfect due to the unpredictability of life events.
Official reports typically define onset as the offender's age at the time of first arrest whereas selfreport measures indicate that onset generally happens three years earlier than data officially
reported. Due to methodological limitations presented with self-reports, it is commonly assumed
that official reports and self-report measures both reflect the age of onset described by official
arrest data. However, the authors of this study disagree with that statement.
When looking at age of onset in sexual offending, data shows that juvenile onset for sex offending is
not typical, suggesting that adult onset is more representative for sexual offenders. Nevertheless,
there is also variance in the age of onset based on the type of sexual crime committed. For example,
offenders who victimize women typically have a younger onset age than those who victimize
children.
This study examined both the official data and actual self-report age of onset for a sample of
convicted sex offenders. The researchers also looked at the gap between these two measures for
determining age of onset and whether the different types of sexual offenses result in a variation in
the onset age gap. Two questions were central. Who is the early offender and to what extent is the
measure of official onset skewed by the offenders ability to avoid or delay detection?
In order to answer these questions, secondary data from a Canadian study were used to compile the
final study analyzed by Lussier and Mathesius. It consisted of a total of 332 males who were all firsttime convicted sex offenders with available criminal history and data on the age of onset of
offending. Interviews were conducted using a computerized questionnaire. The offenders'
correctional files were available to determine onset and detection avoidance. All the information
gathered was coded in a way to maintain the anonymity of the participants.
Actual age of onset, official age of onset, and detection avoidance were measured for each
participant. To calculate the actual age of onset, self-reports, victimization statements, and police
reports were used. The average actual age of onset was found to be 32.1 years old. Criminal arrest
information served as the primary source for the official age of onset. According to these records,
the average age of onset was 39.9 years of age.
Finally, detection avoidance was created by calculating the time lapse between actual onset age and
the date of the first official conviction. The average detection avoidance period was determined to
be seven and a half years. The results showed that a later age of onset in offenders allowed for a
delayed detection when compared to earlier onset offenders. When looking at onset and types of
crime, the age of onset did not vary significantly by type of offender.
With regard to the type of victims, an earlier onset was found for those offending against adults,
females, and strangers. A later onset was found among those targeting children 12 or younger,
males, or victims within their own family environment. A relationship was also found between
detection avoidance and the victim-offender relationship. Lastly, offenders who targeted more than
one victim category experienced longer delays in detection.
This study showed that, on average, there was a gap of approximately seven years between official
and self-report rates of onset. Possible causes include persistence in sex offending and detection
avoidance. Significant diverges were found in detection avoidance, suggesting that it may have
more to do with the victim's characteristics and opportunity presented to them than any other
factor. As a final note, the researchers indicated the importance of having multiple indicators to
differentiate patterns of offending in order to inform policy.