Notes
on the development of Static-2002
2003-01
R. Karl Hanson Department of the Solicitor General of
Canada
David Thornton Sand Ridge Secure Treatment Center Department of Health and Family Services,
WI
The views expressed are those of the authors
and do not necessarily reflect those of the Department of the
Solicitor General of Canada or the Department of Health and Family
Services in Wisconsin. This document is available in French. Ce rapport est disponible en français sous le
titre : Notes sur l'élaboration de
la Statique-2002.
Public Works and Government Services
Canada Cat. No.: JS42-116/2002 ISBN: 0-662-67086-8
AUTHORS NOTE
We would like to thank Ron Coles, Jean
Proulx, Larry Motiuk, Marylee Stephenson, John Reddon, Lea
Studer, Janice Marques, Roxanne Lieb and Lin Song for
access to their original data sets.
Correspondence concerning this report can be
addressed to either author.
R. Karl Hanson Corrections Research Department of the Solicitor General of Canada 340 Laurier Ave., West Ottawa, Ontario Canada K1A 0P8
Telephone: (613) 991 2840
Fax: (613) 990 8295 email: hansonk@sgc.gc.ca
David Thornton Sand
Ridge Secure Treatment Center Department of
Health and Family Services of Wisconsin 1111
North Road Mauston, Wisconsin 53948 U.S.A.
Telephone: (608) 847 1744
Fax: (608) 847 1749 email: thorndm@dhfs.state.wi.us
ABSTRACT
This paper describes the development of a new
risk scale for sexual offenders, Static-2002. Like Static-99 (Hanson
& Thornton, 1999, 2000), Static-2002 is intended to be a widely
applicable risk scale for the prediction of sexual recidivism, which
can be coded using commonly available file information. Preliminary
analyses (n = 2,169; k = 7) suggest that Static-2002 shows
promise, but further research is needed before it can be used in
applied contexts. This description of Static-2002 is presented with
the hope that researchers can examine its utility and predictive
accuracy in new samples.
NOTES ON THE DEVELOPMENT OF
STATIC-2002
Why the need for a
revision?
Static-99 (Hanson & Thornton, 2000) has
been widely adopted as a measure of sex offence recidivism risk,
with routine applications in jurisdictions as diverse as Sweden,
Texas, and Taiwan. Static-99 is intended to assess the long-term
potential for sexual and violent recidivism based on objective,
easily obtainable information, such as official criminal history,
victim characteristics, and age. The 10 items used in Static-99 were
selected from the non-redundant items in two pre-existing risk
scales: The Rapid Risk Assessment for Sex Offence Recidivism
(RRASOR) (Hanson, 1997) and Thornton's Structured Anchored Clinical
Judgement scale (SAC-J) (Grubin, 1998).
Replication studies have found that Static-99
shows levels of predictive accuracy similar to those found in the
developmental samples (Barbaree, Seto, Langton, & Peacock, 2001;
Nunes, Firestone, Bradford, Greenberg, & Broom, 2002; Sjöstedt,
& Långström, 2001). Nevertheless, there are several reasons for
revising the measure. The first is a desire for increased coherence
and conceptual clarity. Scales that have been developed on a purely
empirical basis can be effective in predicting recidivism. However,
if evaluators are to considered variables external to an actuarial
risk scale, then it is necessary to understand what the scale is
already assessing.
Another goal was to improve the consistency
of the scoring criteria. Static-99 was created by combining two
different scales, each with their own coding rules. As well,
Static-99 used the definitions of variables already coded in
existing data sets. Consequently, those learning Static-99 are often
confronted with unanticipated changes in the coding principles
across items. Training would be facilitated and rater reliability
improved by increasing the consistency of the coding rules.
Another concern with Static-99 is that
certain (rare) cases result in counterintuitive scorings. For
example, the score for an offender with a conviction for index
non-sexual violence may decrease if he subsequently reoffends with a
sexual offence.
It was also hoped that by adding new
variables and refining the definitions of the existing variables,
the predictive accuracy could increase. In the absence of a marked
improvement in predictive accuracy, Static-2002 would still be an
improvement over Static-99 if it retained the same levels of
predictive accuracy while being simpler and easier to score.
The overall goals of the revision are the
same as that of the original Static-99 (and RRASOR and SAC-J):
namely, a widely applicable risk scale for the prediction of sexual
recidivism that could be reliably scored from commonly available
information. As with Static-99, it was hoped that the scale would
show similar levels of predictive accuracy for institutional and
community samples of rapists, child molesters and exhibitionists.
The emphasis in scale construction was on the
prediction of sexual recidivism. Preliminary analyses were conducted
on the current data sets in an attempt to create a separate scale
for the prediction of any violent recidivism (including sexual)
among sexual offenders. The resulting violence scale was
sufficiently similar to the sexual recidivism scale that only the
sexual recidivism scale was retained.
OVERALL STRATEGY FOR REVISION
Variables
considered
The selection of variables for Static-2002
was guided by previous research on factors associated with sexual
offence recidivism. Major sources of variables were the Hanson and
Bussière (1998) meta-analysis as well as other empirically developed
sex offender risk scales, such as the SORAG (Quinsey, Harris, Rice,
& Cormier, 1998) and the MnSOST-R (Epperson, Kaul, &
Hesselton, 1998). One important data set contained all sexual
offenders released in British Columbia between 1980 and 1992 (n =
727; Hanson, Broom & Stephenson, 2001). The criminal history
records in the Hanson et al. (2001) data
set were deliberately coded in alternate ways allowing for empirical
comparisons between coding methods (e.g., counting charges versus
sentencing occasions). We also included a number of exploratory
variables that were suggested by the constructs we were attempting
to assess (e.g., age range of victims).
In keeping with the goals of Static-99, a
central concern in variable selection was the ease of data
collection. The only variables considered were the offender's age,
his officially documented criminal history and the characteristics
of the victims of sexual offences (age, relationship to offender,
gender). The Static-99 item "Ever lived with a lover for two years"
was deleted from Static-2002 because of evaluators' concerns that it
was poorly documented in the offender records, and hard to validate
in adversarial contexts. The resulting 22 individual variables were
organized into the following five content areas: age at release,
persistence of sex offending, deviant sexual interests, range of
available victims, and general criminality (see Table 1).
Selecting and
weighting variables
Scale construction was strongly grounded in
the available data, but was not determined by it. There are any
number of possible arrangements of the data that could yield similar
levels of predictive accuracy. Other researchers following the same
general procedure with the same data should identify the same
content areas (and the same univariate relationships), but the
specific cut-points and weightings could vary substantial (e.g.,
"age < 30" versus "age < 35").
The principles guiding the selection and
weighting of items were simplicity and relevance. Whenever possible,
decisions between alternate coding approaches were empirically
based. When two alternate coding methods produced equivalent
predictive accuracy, then the simpler coding method was selected. In
general, simple weights work as well as more complex systems
(Silver, Smith & Banks, 2000).
Table 1 Content areas and variables
considered
Content
area/variable |
Sexual
recidivism predictor? |
Violence
recidivism predictor? |
Age at
release |
+ |
++ |
Sex offence
history
Sentencing occasions for sexual
offences
Age at first arrest for a sexual
offence
Rate of sexual offending
(occasions/age) |
++ |
+ |
Deviant Sexual
Interests
Any non-contact sex offences
Any male victims
Young, unrelated victims |
++ |
0 |
Range of
available victims
Any unrelated victims
Any stranger victims
Age youngest victim
Age oldest victim
Age range of victims
Victims inside and outside the family
|
+
+
?
?
+
+ |
?
+
0
?
?
? |
General
Criminality
Any violation of conditional release
Any prior arrests/charges for anything
Sentencing occasions for anything
Age at first arrest
Years offence free prior to index
offence
Prior non-sexual violence
Index non-sexual violence
Any conviction for non-sexual violence
Age at first arrest for non-sexual
violence |
+ |
++ |
Expected relationship with recidivism: + =
weak (r = .10 to .15 range); ++ = moderate (r = .15 to .20
range); 0 = none; ? = unknown.
Scale construction started by examining the
univariate relationships with the sexual recidivism. Variables
without significant univariate relationships with sexual recidivism
were excluded. The next step was to combine the significant
variables within each content area. Given that the variables within
the content areas were expected to be correlated (e.g., unrelated
and stranger victims), there was no requirement that all the items
within a content area independently contributed to the prediction of
sexual recidivism. Instead, the variable could be retained if it
resulted in any improvement in predictive
accuracy. The inclusion of multiple indicators of similar constructs
should raise the reliability of assessment.
Once the items within a content area were
defined, multivariate analyses were conducted to determine whether
the subscale added incrementally over the subscales already
considered. Subscales that made unique contributions were weighted
so that a unit increase in each subscale was associated with
approximately the same amount of increase in recidivism risk as for
the other subscales (odds ratios in logistic regression or Cox
regression).
None of the data sets contained all of the
variables under examination. Consequently, the analyses started with
the data sets containing the most complete information, and then
approximations would be created in other data sets. The analysis of
the content areas was conducted with all the data available for that
content area.
Several initial scales were tested and
refined across subgroups (total, rapists, child molesters,
extrafamilial child molesters, intrafamilial offenders). Slight
differences were observed across groups (e.g., age was more
important for rapists than extrafamilial child molesters), but none
of the resulting scales showed substantially different levels of
predictive accuracy. Consequently, the definitions/weightings used
were those that appeared to be the most widely applicable.
Samples
An overview of the samples can be found in
Table 2. All the offenders were released from institutions with the
exception of the Manitoba Probation sample and about half of the
offenders from the Washington sample, who received community
sentences. Racial ethnicity was not recorded for most samples, but
given the demographics of the provinces, states and countries from
which they were selected, the offenders can be expected to be
predominantly white. All offenders were adult males (18 years old or
older at time of release).
All samples included information concerning
the outcome variables of sexual and violent recidivism, and all but
one study (Alberta Hospital Edmonton) included survival times. All
studies had information concerning the predictor variables of age
and prior sexual offences. The remaining predictor variables were
missing in at least one study. No study was without missing data on
at least three of the 22 variables.
Table 2 Study characteristics.
Click
on image to enlarge
Canadian Federal -
Pacific Region (CS/RESORS Consulting, 1991; Hanson, et al., 2001). This study followed sexual
offenders released in British Columbia between 1976 and 1992. The
original aim of the study was to compare offenders who received
mandatory community counselling (n = 401) and those released in
earlier years without the benefit of this post-release program (n =
288). Offenders released in the 1983/84 fiscal year
(n = 38) were removed from this sample to avoid overlap
with the other Correctional Service of Canada cohort described
below. Recidivism information was coded in 2000 from Royal Canadian
Mounted Police records. Information was not available concerning
relationship history and victim characteristics.
Canadian Federal
Recidivism Study - 1983/1984 Releases (Bonta & Hanson,
1995a; see also Bonta & Hanson, 1995b). This study examined the
316 sexual offenders included in the complete sample of 3,180
federal offenders released by the Correctional Service of Canada
(CSC) in the fiscal year 1983/1984. Sexual offenders were defined as
those who were released following any sexual conviction. Recidivism
information was collected in 1994 using national criminal history
records maintained by the Royal Canadian Mounted Police (RCMP).
Information was not available for victims, age at first sex arrest,
age at first arrest for violence, and non-contact sex offences.
Sexual sentencing occasions was approximated as 2/3 of convictions.
Canadian Federal 1991
to 1994 Releases (Motiuk, 1995; see also Motiuk & Brown,
1993; Motiuk & Brown, 1996). This study followed a group of
sexual offenders released by CSC between 1991 and 1994. The
offenders in this group were those who were reviewed in 1991 (see
Motiuk & Porporino, 1993) while they were still incarcerated.
Follow-up information was coded from 1994 RCMP records. Information
was not available for breach and time free before index. Sexual
sentencing occasions were approximated as 2/3 of convictions;
non-contact sex offences were approximated by index convictions for
exhibitionism; sentencing occasions for anything were approximated
by twice prison sentences.
Millbrook Recidivism
Study (Hanson, Steffy & Gauthier, 1993b; see also Hanson,
Scott & Steffy, 1995; Hanson, Steffy & Gauthier, 1992,
1993a). This study collected long-term recidivism information (15-30
years) for child molesters released between 1958 and 1974 from
Millbrook Correctional Centre, a maximum security provincial
correctional facility located in Ontario, Canada. About half of the
sample went through a brief treatment program. Recidivism
information was coded from RCMP records in 1989 and 1991.
Information was not available for breach, non-contact sex offences,
time free before index, and age of first violent offence. Sentencing
occasions for sex offences was approximated by 2/3 convictions;
sentencing occasions for anything was approximated by 2/3
convictions for anything.
Institut Philippe
Pinel (Montreal). (Proulx, Pellerin, McKibben, Aubut &
Ouimet, 1995; see also Proulx, Pellerin, McKibben, Aubut &
Ouimet, 1997; Pellerin et al., 1996).
This study focused on sexual offenders treated at a maximum security
psychiatric facility between 1978 and 1993. The Institut Philippe
Pinel in Montreal provides long term (1-3 years) treatment for
sexual offenders referred from both the mental health and
correctional systems. Recidivism information was collected in 1994
from RCMP records. Information was not available concerning stranger
victims, age at first sex offence, breach, non-contact sex offences,
age at first any offence, time free before index, index non-sexual
violence, age at first violent offence. Sentencing occasions for sex
offences was approximated by ½ charges.
Alberta Hospital
Edmonton - Phoenix Program. (Reddon, 1996; see also Studer,
Reddon, Roper & Estrada, 1996). The sexual offenders in this
study were drawn from those treated at the Phoenix (Alberta Hospital
Edmonton) program between 1987 and 1994. The Phoenix program is an
eclectic inpatient treatment program that receives many of its
referrals from federal correctional facilities. Recidivism
information was collected in 1995 using RCMP records. Information
was not available concerning age at first sex offence, breach,
non-contact sex offence, age at first arrest for anything, time free
before index, and all variables concerning non-sexual violence.
Sentencing occasions for sex offences were approximated by 2/3
convictions; sentencing occasions for anything were approximated by
2/3 convictions.
California's Sex
Offender Treatment and Evaluation Project (SOTEP). (Marques
& Day, 1996; see also Marques, Day, Nelson & West, 1993;
Marques, Nelson, West & Day, 1994). The primary aim of this
ongoing study is to examine the efficacy of treatment. The sample
used in the current study included sexual offenders randomly
assigned to treatment (n = 172), matched volunteer controls,
treatment refusers, as well as a general sample of sexual offenders
from the California correctional system (total sample of 1,137). Men
who had offended only against their biological children were not
included. Subjects were admitted to this study between 1985 and
1995; follow-up information was collected in 1995 based on local and
national criminal records, as well as local police and probation
reports. Information was not available concerning age at first sex
offence, breach, non-contact sex offences, sentencing occasions for
anything, age at first arrest for anything, time free prior to
index, and all variables related to non-sexual violence.
Her Majesty's Prison
Service (UK). (Thornton, 1997). This study provided a 16 year
follow-up of all sexual offenders released from Her Majesty's (HM)
Prison Service (England and Wales) in 1979 (n = 573). Recidivism
information was based on Home Office records collected in 1995. Very
few of the offenders in this sample would have received specialised
sexual offender treatment. Information was missing concerning
breach, time free prior to index, and juvenile arrests for sexual
offences.
Washington.
(Berliner, Schram, Miller & Milloy, 1995; Song & Lieb,
1995). This data set was created to evaluate Washington State's
Special Sex Offender Sentencing Alternative (SSOSA), which allows
judges to sentence sex offenders to community treatment. To be
eligible for SSOSA, offenders must be facing their first felony
conviction for sexual crimes other than first or second degree rape.
The sample consisted of 287 offenders who received SSOSA and 300 who
were statutorily eligible for SSOSA but did not receive it. The
majority of the sample was White (85%). Offenders were convicted
between January 1985 and June 1986, with follow-up data collected in
December, 1990. Information was missing concerning breach, time free
prior to index and all variables concerning non-sexual violence.
Sentencing occasions for sex offences were approximated by 2/3
convictions; any non-contact sex offences was approximated by "index
convictions were only exhibitionism or peeping"; sentencing
occasions for anything were approximated by 2/3 convictions.
Manitoba
Probation. (Hanson, 2002). This follow-up study was conducted as
an evaluation of a risk scale used by probation officers in
Manitoba, Canada. The 202 offenders were consecutive admissions
to probation between May, 1997 and February, 1999. Recidivism
information was collected in November, 2000, based on RCMP records.
Unlike the RCMP records used in the other studies (which included
only charges and convictions that went to court), the RCMP records
for the Manitoba sample included unresolved charges and cases
currently under police investigation. The demographic, victim and
offence information was collected by the probation officers in the
course of their normal duties. The criminal history variables needed
for coding Static-99 were coded by trained research assistants
(median r = .93; median Kappa = .87). Information was missing
concerning male victims, breach, age at first arrest for anything,
time free prior to index, and age at first arrest for violence.
Sentencing occasions for sex offences was approximated by 2/3
convictions; any juvenile sexual offences was approximated by "sex
offence committed prior to age 20".
Plan of analysis
There are two common approaches for analysing
data from multiple data sets. One approach is to ignore differences
between samples and combine the results into one big sample
(combined approach). The other option identifies the relationships
within each sample, then summarizes the results across samples
(nested approach). The summary of nested effects can be accomplished
through meta-analysis (Hedges & Olkin, 1985), or certain
statistical procedures (e.g., Cox regression with each sample as a
separate strata). The combined and the nested approaches often yield
equivalent results, but when differences occurs, the
nested/meta-analytic results are the more dependable. Combining
samples can artificially increase effects (e.g., the sample with the
largest proportion of high risk offenders is also the sample
followed for the longest period of time) or decrease effects (e.g.,
the sample with the largest proportion of low risk offenders has the
broadest criteria for recidivism). Given that difference results
were observed for some variables using the combined versus the
nested approaches, the nested approach was adopted as the primary
method of data analysis.
RESULTS
In the combined sample, rapists were slightly
higher risk to sexually recidivate (16%) than were child molesters
(13%, p < .05), but the effect was largely due to the relatively
low recidivism rates of intrafamilial child molesters (5%) compared
to extrafamilial child molesters (18%). The rates for any violent
recidivism (including sexual) were higher for rapists (34.0%) than
extrafamilial child molesters (23.8%) and incest offenders (10.9%).
All of the individual variables in Table 1
were significantly related to sexual recidivism with the following
exceptions: age youngest victim, age oldest victim, age range of
victims, victims inside and outside the family, and index non-sexual
violence. Consequently, these five variables were excluded from
further analysis.
Some comments on the coding of specific
variables is given below.
Age. Age was more
strongly related to violent recidivism than sexual recidivism. As
well, the age effect was stronger for rapists than child molesters.
Nevertheless, there was a significant decline in all forms of
recidivism with age (see Hanson, 2001). The coding selected (see
Appendix A) was intermediate between the codings that appeared
optimal for predicting sexual recidivism among child molesters (the
lowest weights) and predicting violent recidivism in the total
sample (the highest weights).
Persistence of sexual
offending. Three variables were considered as indicators of the
persistence of sexual offending: the number of prior sexual
offences, the rate of sexual offending, and the age of first arrest
for a sexual offence.
In order to choose between the various
possible codings of prior sexual offences, the CSC Pacific data set
(Hanson et al., 2001) was coded with four
different definitions: arrests, charges, convictions, and sentencing
occasions (for both index and prior offences). The number of index
offences (whatever the definition) was not related to sexual offence
recidivism. Prior sexual offences, however, consistently predicted
recidivism, with the largest correlation being for sentencing
occasions (r = .21, with r = .19 for the other three
codings). Friendship, Thornton, Erikson and Beech (2001) found that
in the UK records, sentencing occasions were more reliably recorded
than were other indicators of prior offending. Consequently,
sentencing occasions was selected because it was not only the most
accurate, but also the simplest.
Examination of the cross-tabulation of prior
sentencing occasions and recidivism suggested the following coding:
0 = 0; 1 = 1; 2, 3 = 2; 4 or more = 3. For those data sets using
other definitions of prior sexual offences, the number of prior
sentencing occasions was estimated using the ratios between
convictions/charges/sentencing occasions observed in the CSC-Pacific
data set: 1 sentencing occasion = 1.5 convictions or 2 charges.
The rate of sexual offending was created by
dividing the total number of sentencing occasions for sexual
offenses by the offender's age at release. Examination of the
distribution suggested a useful break point of once every 15 years
(.0667).
The age at first arrest for a sexual offence
was strongly related to sexual recidivism. Given that this variable
was correlated with both the offender's current age and the number
of prior sexual offences, it did not independently contribute when
these other variables were considered. Examination of the limited
available data suggested that the existence of arrests both as a
juvenile and as an adult captured enough meaningful variation to
warrant inclusion in the Persistence subscale.
Deviant sexual
interests. Three variables were considered as indicators of
deviant sexual interests: any male victims, any non-contact sexual
offences, and multiple young victims (defined as two or more victims
less than age 12, at least one of which must be unrelated). All
three variables predicted sexual recidivism, both individually and
in combination (only one data set, however, contained all three
variables - HM Prison Service). Consequently, all three variables
were retained and given equal weight (0 = no, 1 = yes).
Range of
victims/Relationship to Victims. Previous research has
demonstrated that having unrelated victims and strangers as victims
were both associated with increased risk for sexual recidivism. One
explanation of these findings is that offenders who are willing to
victimize stranger have a wider range of potential victims than
those who offend only within the family. Consequently, it was
hypothesized that having victims of widely different ages could also
be a risk marker for sexual recidivism. This was not the case. In
the current data sets, the age range of victims was unrelated to
sexual recidivism. As well, the offenders who had victims both
inside and outside the family (another indicator of range of
available victims) were no different in their sexual recidivism
rates than offenders who selected only unrelated victims.
Given that the only two variables retained
from this section were Any Unrelated Victims and Any Stranger
Victims, the section was renamed "Relationship to Victims". Both
items independently contributed to the prediction of sexual
recidivism (p < .001 using Cox regression). In the combined
sample, the sexual recidivism rate was 6% for purely incest
offenders, 13% for those who victimized acquaintances, and 21% for
those who victimized strangers. One point was assigned to Any
Unrelated Victims (0/1) and for Any Stranger Victims (0/1),
resulting in a range of 0 to 2.
General
criminality. The variables defining general criminality (breach,
time free before index, age at first arrest, number of prior
offences, prior non-sexual violence) were all intercorrelated
(median r = .44) and factor analysis strongly suggested a single
factor (eigenvalues of 2.64, .81, .68, .52, .35). Prior non-sexual
violence was selected as the measure of non-sexual violence because
it was a slightly stronger predictor of sexual recidivism than Any
non-sexual violence. As previously mentioned, Index Non-Sexual
Violence was not significantly related to sexual recidivism in the
combined data set, and was excluded. Age at first arrest was also
excluded because the relationships with sexual recidivism were
inconsistent across data sets, and information concerning juvenile
records was not well recorded.
The number of prior involvements with the
criminal justice system was coded as follows: 0 = no prior charges
for anything; 1 = any prior charges but less than 3 sentencing
occasions; 2 = 3-13 prior sentencing occasions; 3 = 14 or more prior
sentencing occasions. The other variables indicative of general
criminality were as follows: Any Breach of Conditional Release (0 =
none/1 = any), Any prior sentencing occasion for non-sexual violence
(0 = none/1 = any), and less than 4 years at liberty prior to the
index offence (0 = more than 4 years/1 = less than 4 years).
Combining and
weighting subscales.
Sufficient information was available to
compare the content areas in 6 of the 10 data sets (CSC -
Pacific Region and CSC 83/84 did not have victim information, SOTEP
lacked criminal history information, and Alberta Hospital Edmonton
lacked survival dates). The six data sets had a total sample of
1,783 with 258 sexual recidivists.
Each of the five content areas independently
predicted sexual recidivism (see Table 3). The independent
contributions were tested using Cox regression with samples as
strata (SPSS, Version 10, 1999). Cox regression is a form of
survival analysis that controls for time at risk, as well as both
categorical and ordinal covariates (see Cox & Oakes, 1984). By
dividing the analysis by strata the results were equivalent to the
nested/meta-analytic approach.
Table 3 Contribution of each subscale to the prediction
of sexual recidivism (Cox regression).
Content area/subscale (range) |
B (SE) |
Wald |
Exp(B) |
Age (0 - 3) |
.340 (.073)
|
21.7*** |
1.40 |
Persistence of sex offending (0 - 3) |
.238 (.073) |
10.7*** |
1.27 |
Deviant sexual interests (0 - 3)
|
.304 (.108) |
7.9** |
1.36 |
Relationship to victims (0 - 2) |
.439 (.109) |
16.2*** |
1.55 |
General Criminality (0 - 3) |
.271 (.086) |
9.9** |
1.31 |
** p < .01; ***p < .001.
The exponent of the regression coefficients
is equivalent to an odds ratio. These exponents (eB) can be interpreted as the proportion
increase in recidivism rates for unit increase in the subscale,
after controlling for the other content areas. The initial analysis
found that the odds ratios for the Persistence of Sex Offending
(1.19) and the General Criminality (1.20) subscales were somewhat
smaller than for the other three subscales (range of 1.41 - 1.52).
Consequently, these two subscales were recoded so that unit
increases in all subscales resulted in similar increases in the
sexual recidivism rate. For the Persistence subscale, the range was
reduced to 0 - 3 (originally 0 - 5) and for the General Criminality
subscale, the range was reduced to 0 - 3 (originally 0 - 6). The
resulting exponents, shown in Table 3, suggested a 30% to 40%
relative increase for each increase in the scale score. In the
combined sample, for example, a score of 2 corresponded to a 4.8%
recidivism rate and a score of 3 corresponded to a rate of 6.4%
(6.5/4.8 = 1.35).
The final scale for Static-2002 is described
in Appendix A.
Scale comparison
To estimate the predictive accuracy of
Static-2002, it was compared to its subcomponents/earlier versions:
namely, RRASOR (Hanson, 1997) and Static-99 (Hanson & Thornton,
2000; Phenix, Hanson & Thornton, 2000). Direct comparisons were
not possible because none of the samples contained all the
variables; consequently, comparisons were conducted using
approximations for each scale. Static-99 was accepted if there were
3 or less missing items (out of 10). Static-2002 was accepted if
there were 5 or less missing items (out of 13), provided that the
missing items were not all of the same type (e.g., not all the
criminal history items, or all the victim information). If an item
was missing, it was scored "zero". RRASOR was scored only if all
four variables could be estimated.
None of the scales were computed for the
CSC-Pacific and CSC-83/84 samples because victim information was not
available. Unfortunately, these were also the only two samples (n =
1,000) that included the variables "breach" and "time free prior to
index". Consequently, these two variables were missing for all the
Static-2002 scores. The following analyses should, therefore, be
considered only as a rough guide to the relative predictive accuracy
of the measures. In particular, the analyses would be expect to
underestimate the predictive accuracy of Static-99 and Static-2002,
while providing reasonable estimates of the accuracy of RRASOR.
Average values for the scales are presented
in Table 4. All three measures were positively skewed, although the
amount of skew was less for Static-2002 (.33, SD of skewness = .053)
than for RRASOR (.80) and Static-99 (.59).
Table 4 Average scores on RRASOR, Static-99, and
Static-2002.
For sexual recidivism, the predictive
accuracy of Static-2002 was similar to that of Static-99 (ROC areas
of .69 to .73 range; see Table 5). In the full sample,
Static-2002 demonstrated an ROC area of .711 compared to an ROC area
of .701 for Static-99 (Z = 1.14, p > .10, using Formula
3 from Hanley & McNeil, 1983). An advantage of Static-2002,
however, was that it showed little variability across samples (Q =
5.65, p >.40) in comparison to Static-99 (Q = 14.08, p <
.025). For Static-99, the lowest predictive accuracy was found for
the two community samples (Washington and Manitoba, ROC areas of .59
for both), and the highest predictive accuracies were for the CSC
91/94 sample (.77) and the Alberta Hospital Edmonton treatment
sample (.76). In contrast, the range for Static-2002 was from .65
(Millbrook) to .77 (CSC 91/94, Alberta Hospital Edmonton).
Static-2002 predicted sexual recidivism as well for child molesters
(.70) as rapists (.72).
Table 5 Sexual recidivism: Predictive accuracy of
RRASOR, Static-99 and Static-2002.
|
Average ROC
areas |
|
|
Scale |
Unweighted Mean
(SD) |
Weighted Mean (SD) |
N (k) |
Q |
Full Sample |
|
|
|
|
RRASOR |
.678 (.060) |
.677 (.015) |
2857 (7) |
8.36 |
Static-99 |
.688 (.076) |
.701 (.016) |
2326 (7) |
14.08* |
Static-02 |
.716 (.046) |
.711 (.016) |
2142 (7) |
5.65 |
Child Molesters |
|
|
|
|
RRASOR |
.671 (.076) |
.690 (.017) |
2094 (7) |
12.37 |
Static-99 |
.700 (.088) |
.720 (.018) |
1606 (7) |
16.24** |
Static-02 |
.687 (.084) |
.702 (.020) |
1472 (7) |
9.50 |
Rapists |
|
|
|
|
RRASOR |
.693 (.134) |
.711 (.025) |
730 (6) |
22.94*** |
Static-99 |
.671 (.133) |
.737 (.027) |
541 (6) |
26.80*** |
Static-02 |
.734 (.091) |
.722 (.031) |
496 (6) |
6.53 |
*p < .05; **p < .01; ***p < .001 k = number of studies
For any violent recidivism (see Table 6), the
predictive accuracy of Static-2002 (.71) was greater than the
predictive accuracy of Static-99 (.69; Z = 3.54, p < .01) and
RRASOR (.62). For all three measures, the amount of variability
across samples was no more than would be expected by chance. The
average ROC areas for violent recidivism were somewhat higher for
child molesters than rapists, but the differences were not
significant for Static-2002 (Q = 0.37, p > .25), Static-99 (Q =
1.50, p > .20) or RRASOR (Q = 3.77, p < .10).
Table 6
Violent
recidivism: Predictive accuracy of RRASOR, Static-99 and Static-2002.
|
Average ROC areas |
|
|
Scale |
Unweighted Mean
(SD) |
Weighted Mean (SD) |
N (k) |
Q |
Full Sample |
|
|
|
|
RRASOR |
.622 (.034) |
.622 (.013) |
2860 (7) |
4.28 |
Static-99 |
.684 (.044) |
.687 (.013) |
2329 (7) |
8.72 |
Static-02 |
.712 (.042) |
.713 (.013) |
2143 (7) |
8.92 |
Child Molesters |
|
|
|
|
RRASOR |
.638 (.041) |
.641 (.016) |
2095 (7) |
4.96 |
Static-99 |
.693 (.063) |
.694 (.017) |
1607 (7) |
11.52+ |
Static-02 |
.711 (.046) |
.703 (.017) |
1472 (7) |
7.29 |
Rapists |
|
|
|
|
RRASOR |
.592 (.051) |
.587 (.023) |
732 (6) |
3.65 |
Static-99 |
.657 (.062) |
.657 (.025) |
583 (6) |
4.04 |
Static-02 |
.687 (.047) |
.684 (.026) |
497 (6) |
2.70
|
+p < .10,
all other Q statistics were associated with probabilities of >
.10.
DISCUSSION
Static-2002 showed similar levels of
predictive accuracy to Static-99 for the prediction of sexual
recidivism. The initial analyses suggested that the new items could
add valuable information, but, given that large amounts of missing
data, further research is necessary to determine whether the new
items/scoring result in a noticeable improvement in predictive
accuracy.
The present study confirms previous results:
Static-99 had slightly higher predictive accuracy than RRASOR, and
the predictive accuracy of both scales was similar for rapists and
child molesters. Such a finding is not surprising given that three
of the seven samples had been previously used in the development of
Static-99. The current study, however, includes new Static-99 data
for four new data sets (n = 1,319) or 61% of the total sample
(average predictive accuracy of .68 in these four data sets, range
of .59 to .77).
Even though the level of predictive accuracy
was similar, Static-2002 has potential advantages over Static-99.
Static-2002 predicted any violent recidivism as well as it predicted
sexual recidivism, and predicted violent recidivism better than
Static-99. Static-2002 was less variable than Static-99 across
settings. As well, the content areas of Static-2002 have increased
conceptual clarity compared to Static-99.
Conceptual clarity is important for
evaluators who wish to consider whether external factors should be
used to adjust the risk level suggested by an actuarial tool.
Researchers may be able to improve the predictive accuracy of
Static-2002 on purely empirical grounds by including other
variables, such as those related to childhood behaviour problems
(e.g., SORAG, Quinsey et al., 1998), or
lack of cooperation with supervision (e.g., Hanson & Harris,
2000). The greatest advances in risk assessment, however, will come
from accurate explanations for recidivism. Research is required to
established the construct validity of the content areas of
Static-2002, and, more importantly, identify the causes of
recidivism. Prior offending is a good predictor variable, but it is
poor theoretical variable. Events that happened twenty years ago
cannot compel future crimes. Instead, researchers need to identify
the current life situations and the enduring characteristics that
predispose certain individuals to offend sexually, whether they be
memories, habits, values, cognitive deficits, or unfortunate life
choices.
Although Static-2002 shows promise, further
research is necessary before it can be used in applied contexts.
Specifically, the results need to be replicated with independent
data sets. Given that the major utility of static risk scales is to
judge long-term recidivism potential, the replication studies should
include a follow-up period of at least 10 years (15 years
preferably). It is likely that the replication studies would need to
include a combined sample size of over 1000 sexual offenders (200 to
400 in each study) before it is possible to associate specific risk
levels to specific ranges of scores.
As with Static-99, Static-2002 was not
intended to provide a comprehensive assessment of recidivism risk.
There are many factors associated with sexual recidivism, such as
sexual preoccupations and access to victims (Hanson & Harris,
2000), that evaluators may want to consider. How best to combine
static, historical factors with dynamic (changeable) risk factors
remains an important topic for future research.
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APPENDIX A Coding rules
for Static-2002
The following should be considered only as a
general overview of the coding rules of Static-2002. Detailed coding
rules are currently being developed. Researchers wishing to use
Static-2002 should contact either Karl Hanson or David Thornton for
the most recent version of the coding rules before proceeding.
Although the items may appear simple, previous experience with
Static-99 suggests that careful attention to the coding rules is
necessary to obtain adequate reliability.
Static-2002 is intended for offenders with an
index sexual offence who have an opportunity to reoffend by virtue
of receiving a community sentence or by release from a custodial
sentence. They must be males, age 18 or older, who have committed a
sexual offence against an identifiable victim.
Age at release (0
- 3)
18 to 24.9 = 3
25 to 34.9 = 2
35 to 49.9 = 1
50 or older = 0
Use the age of the offender at the time that
the risk assessment is to be used.
Persistence of sexual
offending (0 - 3)
This section includes three variables: a)
prior sentencing occasions for sexual offences (0 - 3), b)
arrests for sexual offences as both an adult and a juvenile (0/1),
and c) rate of sexual offences (0/1). Code each of the individual
variables, then recode the subscale as follows:
Raw score |
Subscale score |
0 |
0 |
1 |
1 |
2, 3 |
2 |
4, 5 |
3 |
Prior sentencing
occasions for sexual offences
0 = 0
1 = 1
2, 3 = 2
4 or more = 3
A sentencing occasion is when the offender
attends court, admits to the offence or is found guilty, and
receiving some form of sanction (fine, prison, conditional
sentence). Offenders may be convicted of more than one offence at
the same sentencing occasion. In England, an official caution count
as one sentencing occasion. Count both adult and juvenile sentencing
occasions.
Offenders may go to court and receive more
than one sentence for a single crime spree. In this case, all the
convictions related to the same crime spree count as one sentencing
occasion. For two sentencing occasions to be considered distinct,
the offender must have committed a crime and been sanctioned for it
prior to committing the second crime (and being sanctioned for it).
When the offender is convicted for a crime that was committed prior
to his previous conviction, the new conviction is considered
pseudo-recidivism and is not counted separately.
Offences are considered as sexual based on
the behaviour, not the name. For example, Assault plead down from
Sexual Assault would still count as sexual if the motivation for the
original offence was sexual. As with Static-99, Static-2002 is
intended for offenders with at least one identifiable victim. It
does not apply to purely prostitution offenders, although
prostitution offences would count as sexual offences if the offender
had a record for any Category A offences (see Static-99 coding
rules; Phenix, Hanson & Thornton, 2000).
Arrest for sexual
offences as juvenile
Arrest prior to age 18 and
conviction after age 18 = 1
No arrest for a sexual
offence prior to age 18 = 0
This items is only scored for offenders who
have a conviction for a sexual offence as an adult. It is not scored
for juvenile offenders who are released after age 18. The adult
conviction must be for different behaviour than that which lead to
the arrest as a juvenile.
Rate of sexual
offending
Less than one sentencing
occasion every 15 years = 0
One or more sentencing
occasions every 15 years = 1
This is calculated by summing all the
sentencing occasions for sexual offences (including index) and
dividing that number by the offender's age at release. For example,
if the offender was 29 years old and have one prior sexual offence,
his rate would be (1 + 1)/29 = .06897, and he
would receive the point for "high rate".
Deviant sexual
interests (0 - 3)
This section contains three items: a) any
convictions for non-contact sexual offences (0/1), b) any male
victims (0/1), and c) young, unrelated victims (0/1). The three
items are summed to make a total score that ranges from 0 to 3 (no
recode).
Non-contact sexual
offences
Any conviction for a
non-contact sexual offence = 1
None = 0
This is the same as the Static-99 item. Count
only convictions for obscene phone calls, internet luring,
possession of child pornography, exhibitionism, and voyeurism. Do
not count prostitution related offence or other offences without an
identifiable human victim.
Any male victims
Any male victims = 1
None = 0
Same as Static-99.
Young, unrelated
victims (0, 1)
Two or more victims less
than age 12, one of which must be unrelated
= 1.
Otherwise = 0
This item is intended as a proxy for sexual
interest in children. The offender receives the point if he has two
separate victims who have yet to obtain their 12th birthday. One of the victims must be
unrelated. If all the victims are related, or if there is only one
victim less than age 12, the offender gets a score of zero.
Relationship to
victims of sexual offences (0 - 2)
This sections contains two items: Any
unrelated victims (0/1) and any stranger victims (0/1). Stranger
victims are also unrelated. The items are summed to get a subscale
score that can range from 0 to 2.
Any unrelated
victims
Any unrelated victims = 1
None = 0
Related general means "too close to marry",
but it also includes 1st cousins,
nephews and spouses. This is the same item as in Static-99 (see
Phenix et al., 2000).
Any stranger
victims
Any stranger victims = 1
None = 0
The relationship is consider as one between
strangers if the offender and victim did not know each other 24
prior to the sexual offence.
This is the same item as in Static-99 (see
Phenix et al., 2000).
General
Criminality (0 - 3)
This subscale contains four items: a)
sentencing occasions for anything (0 - 3), b) any breach of
conditional release (0/1), c) less than 4 year free prior to
conviction for index offence (0/1), and ) any prior conviction for
non-sexual violence. The raw score is recoded as follows:
Raw score |
Subscale score |
0 |
0 |
1, 2 |
1 |
3, 4 |
2 |
5, 6 |
3 |
Arrest/Sentencing
occasions for anything
No prior arrest for
anything = 0
Any arrest, but less than
3 sentencing occasions for anything = 1
3 - 13 sentencing
occasions = 2
14 or more sentencing
occasions = 3
Do not count the index offence(s). Count
sexual and non-sexual sentencing occasions. Do not count very minor
offences for which it would be impossible to go to jail or to
receive a community sentence (e.g., drinking under age, speeding).
Breach
Any breach of conditional
release = 1
None = 0
This item is scored "1 = yes" if the offender
has ever been charged with an offence related to failure to conform
to the demands of bail, parole, probation or community supervision
(e.g., failure to comply with probation, parole revoked). It is also
scored if the offender is arrested for a new offence while on a
community supervision order (including bail, parole, probation).
Years Free Prior to
Index
Less than 36 month free
prior to committing the sexual offence that resulted in the index
conviction, or
Less than 48 months free
prior to conviction for index sex offence = 1,
More than 48 months free
prior to index conviction and
More than 36 months free
prior to committing the sexual offence that resulted in the index
conviction = 0
Calculate the number of months between the
date of release into the community from the previous involvement
with the law, and the date of the most recent sex offence (the index
sex offence). For offenders who received custodial sentences, the
release into the community would be the release date from prison.
For offenders sentenced to the community, it would be the date of
sentence. Arrest and charges count as involvements with the law,
even if the offender was not convicted.
Two dates are associated with the index
sexual offence: a) the date the offence occurred, and b) the date
the offender was convicted. The offender gets one point if either
the time span between release and reconviction was less than 48
months, or the time span between release and sexual reoffending was
less than 36 months.
Count juvenile offences for offenders who
were less than 22 years of age at the time of conviction for the
index sexual offense.
Prior violent
non-sexual convictions
Any prior conviction for
non-sexual violence = 1
No prior convictions = 0
Violent non-sexual offences are those that
involve confrontation with the victim, such as robbery, assault, and
murder, as well as arson and threatening. In contrast to Static-99,
count only violent offences that were not sexually motivated. If an
offender attempts a sexual assault, but is only convicted of
Assault, the assault would count as a sexual offence and would not
count as non-sexual violence. The criminal event that results in the
conviction for non-sexual violence must be different from the
criminal event that resulted in a conviction for sexual offending.
The conviction for non-sexual violence must occur prior to the index
sexual offence. Do not count convictions for non-sexual violence
that are included in the index cluster of offences (i.e., the crime
spree that included the index sex offence).
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