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St Nicholas Hospital, Newcastle upon Tyne, UK
Correspondence: Professor D. Grubin, St Nicholas Hospital, Gosforth, Newcastle upon Tyne NE3 3XT, UK. E-mail: don.grubin{at}ncl.ac.uk
Declaration of interest None. Funding detailed in Acknowledgements.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
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Aims To investigate the utility and accuracy of polygraphyin post-conviction testing of community-based sex offenders.
Method A self-report measure examined the experiences of offenders with polygraphy.
Results Based on self-report, the polygraph’s accuracy was approximately 85%. False negatives and false positives were not associated with demographic characteristics, personality variables or IQ. The majority of offenders found the polygraph to be helpful in both treatment and supervision. Nine percent of offenders claimed to have made false disclosures; these individuals had higher scores on ratings of neuroticism and lower scores on ratings of conscientiousness.
Conclusions These results supportthe view thatthe polygraph is both accurate and useful in the treatment and supervision of sex offenders.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
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METHOD |
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TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
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Risk
One hundred and sixty-one participants were scored on Static-99
(Hanson & Thornton, 2000),
a widely used actuarial instrument that provides an estimate of the
probability of sexual and violent recidivism for adult males (the other 15
individuals could not be scored on this instrument). Ten individuals were
scored by two raters unaware of each other’s results, with perfect
agreement between them. Based on Static-99 ratings for these 161 individuals,
93 participants (58%) were assessed as low risk, 46 (29%) as medium-low risk,
19 (12%) as medium-high risk and 3 (2%) as high risk.
Personality
The Revised NEO Personality Inventory (NEO;
Costa & McCrae, 1992) is a
self-report questionnaire that assesses normal personality dimensions based on
a five-factor model: neuroticism (N), extraversion (E), openness to experience
(O), agreeableness (A) and conscientiousness (C). Valid NEO profiles were
obtained for 152 participants (86%). Overall, scores were in the high range
for neuroticism (mean 87, s.d.=21), the average range for extra-version (mean
101, s.d.=16) and agreeableness (mean 120, s.d.=15) and in the low range for
openness (mean 100, s.d.=15) and conscientiousness (mean 114, s.d.=17).
IQ
The second edition of the National Adult Reading Test (NART–2;
Nelson & Willison, 1991)
was used to provide an estimate of IQ. Thirteen participants did not complete
this test. For the remaining sample the mean IQ was 102 (s.d.=11.9, range
75–128).
Previous experiences of the polygraph
A 12-item survey, the Previous Experiences of the Polygraph Questionnaire
(PEPQ), was developed for the study to gather descriptive information about
participants’ previous experiences and perceptions of the polygraph (the
PEPQ is included as a supplement to the online version of this paper). The
questionnaire is divided into three sections. The first section addresses
false positive and false negative rates, false admissions and the use of
countermeasures; the second addresses the extent to which the participants
consider the polygraph to be helpful in assisting them to avoid risk
behaviours and re-offending and to engage in treatment; and the third section
investigates the participants’ perceptions of polygraph accuracy
(further information available from the author on request).
Procedure
All participants were taking part in treatment programmes in which
polygraphy was a condition of participation, and were approached while
attending their regular treatment groups. They were informed that the purpose
of the research was to investigate the value of the polygraph in a
post-conviction context. They were assured of confidentiality, and all gave
their signed informed consent. Participants were seen on a single occasion for
up to 60 min, during which they completed the PEPQ, either by themselves or
with other participants. They were then interviewed about their present
circumstances and past experiences of the polygraph; the NART–2 was
administered at this time.
Ethical approval
The study was submitted to the Northumberland, Tyne and Wear research
ethics committee. Because the study was carried out in the USA it fell outwith
the committee’s remit, but its memebrs indicated that it would have been
considered favourably. This was taken into account by each treatment centre in
its review of the protocol.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
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When the 126 individuals who had taken polygraph tests are considered rather than the number of tests they reported completing, 27 (21%) stated that they had been wrongly reported as deceptive when telling the truth on at least one occasion, and 6 (5%) that they had been wrongly reported as being truthful when they had in fact been lying (Table 2). There was no overlap between these individuals.
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False positive cases
Individuals who reported telling the truth but were wrongly labelled as
deceptive (false positive; n=27) were compared with those who said
they had been correctly classified as telling the truth (true negative;
n=64), as well as with those who reported being correctly detected as
being deceptive (true positive; n=29). Relevant variables were
grouped into two categories: historical (age, ethnic origin, previous
psychological and psychiatric history, educational attainment, number of
previous polygraph tests, and risk) and psychological (personality, IQ).
Univariate analyses did not yield any significant difference between the
groups in respect of any of these variables.
False negative cases
Individuals who claimed they had been deceptive but were classified as
‘no deception indicated’ (false negative; n=6) were
compared with those who reported being deceptive but accurately labelled as
such (true positive; n=29), and with those who said they had been
correctly labelled as non-deceptive (true negative; n=64). Univariate
analyses did not yield any significant results.
Utility
Of the 126 offenders who had been polygraph tested, 114 fully completed the
PEPQ. Of these 114, 50 (44%) reported that they were more truthful with their
probation officers and treatment providers than they otherwise would have been
because of the polygraph; 39 (34%) reported that it assisted them in being
more truthful about their behaviour to family and friends. Similar results
were found in relation to the 45 participants who had not yet been tested and
fully completed the PEPQ, with 20 (44%) and 16 (36%) respectively indicating
that the expectation of a polygraph test increased their disclosures to
probation officers and to family and friends.
Regarding behaviours associated with offending, 71 (56%) of the 126 individuals who had previously been polygraph tested reported that the polygraph was moderately to extremely helpful in assisting them to avoid re-offending, re-offending, 80 (63%) that it was useful in assisting them to avoid risk behaviours and 84 (67%) that it was generally helpful in respect of treatment; similar responses were given by those awaiting their first examinations (Fig. 1).
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Information was available for 173 men regarding specific risk behaviours:
57 individuals (33%) reported that they were less likely to masturbate to
deviant (offence-related) fantasies, 53 (31%) that they were less likely to
have contact with children or potential victims, 47 (27%) that their use of
drugs and alcohol was reduced, and 44 (25%) that they were less likely to use
or buy pornography. However, a significantly greater proportion of those who
had undergone polygraph testing, compared with those awaiting their first
test, reported that they were less likely to visit places to view children (37
. 5, 
2=5.9, d.f. 1, P=0.01) and to engage in
other more general risk behaviours (18 . 1, 2=4.2, d.f.=1,
P=0.04).
Information was available for 165 men regarding their perception of the accuracy of the polygraph. No difference was found between participants who had previously had a polygraph test and those who had not. Overall, 16 participants (10%) considered it to be no more accurate than chance, 15 (9%) ‘slightly’ accurate, 73 (44%) ‘moderately’ accurate and 63 (38%) as being ‘quite’ to ‘extremely’ accurate.
Sanctions
Twenty-seven (22%) out of 121 men who had completed a post-conviction
polygraph test reported experiencing a direct sanction because of its result
or a disclosure made during the test; the most common of these involved having
to address additional issues in treatment or supervision (78%), although two
individuals claimed that their treatment was terminated and two that their
contact with their families was reduced. There was no relationship between
having experienced a sanction and claiming to have had a false positive result
(2=3.07, d.f. 1, P=0.08).
To test whether having been sanctioned or erroneously classified (false positive or false negative) affected the participant’s perception of the polygraph’s utility, an overall ‘helpfulness’ variable was created by combining the scores of the three utility scales. No difference in perception of utility was found between those who experienced sanctions and those who did not (t(111)=0.38, P=0.7), nor was there a difference between those who reported being false positives and true negatives, or between the false negatives and true positives.
Countermeasures and false admissions
Only two participants (2%) claimed to have used drugs to beat the
polygraph. Both also claimed to have previously been deceptive without being
detected. Twelve participants (10%) reported making false admissions regarding
their behaviour at some stage during a post-conviction polygraph test, of whom
only 5 claimed to have been wrongly labelled as being deceptive. The main
reasons given for false admissions were the fear of getting in trouble with
probation officers in three cases, and feeling pressured by the polygraph
examiner in another three cases. Other reasons were wanting to make a good
impression, ‘confusion’, ensuring that the test was passed, and
wanting to demonstrate commitment to therapy.
A significant difference was found when a one-way between-groups
multivariate analysis of variance was performed using the five NEO domain
scores as dependent variables and ‘having made a false admission’
as the independent variable (F(5,96)=2.46,
P<0.01). When results for the dependent variables were considered
separately, two reached statistical significance using a Bonferroni-adjusted
alpha level of 0.01: neuroticism (F(1,102)=10.08,
P<0.01) and conscientiousness (F(1,102)=7.85,
P<0.01), with the false confessors having higher levels of
neuroticism (104 . 84) and lower levels of conscientiousness (101 .
116).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
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Utility of post-conviction polygraph testing
Our results are consistent with other studies examining the utility of
post-conviction polygraph testing in sex offenders, which typically report
fuller histories of deviant sexual behaviour, admissions of previously unknown
offences and victims, and increased disclosure of high-risk behaviours
(Emerick & Dutton, 1993;
Ahlmeyer et al, 2000;
Harrison & Kirkpatrick,
2000; Hindman & Peters,
2001; Grubin et al,
2004; Madsen et al,
2004). It has been argued that increased disclosure by offenders
enables improved identification of treatment targets, encourages engagement by
helping to overcome denial, and assists offenders in adhering to relapse
prevention plans (Blasingame,
1998; English et al,
2000; Grubin et al,
2004). Our findings indicate that polygraphy can have a
therapeutic role as well as the more usually perceived function of
‘detecting lies’. Indeed, confirmation that an individual is being
honest in treatment and supervision, particularly in contexts where risk is a
real issue, can be a critical element in the treatment process.
Accuracy
Although an emphasis on utility in post-conviction settings is
understandable, polygraph accuracy cannot be ignored. If those tested do not
believe that polygraphy works, they will be less likely to disclose relevant
information during a test. In addition, a knowledge of accuracy rates is
required to make sense of apparent deception in the absence of disclosure.
Those tested as well as those who rely on test results must have confidence in
the validity of the technique if it is to be viable clinically.
The literature contains conflicting accounts of polygraph accuracy, with many studies criticised for their methodological weaknesses (Furedy, 1996; Lykken, 1998; Cross & Saxe, 2001). A recent definitive review carried out by an expert panel appointed by the US National Academy of Sciences concluded that the best estimate of polygraph accuracy falls between 81% and 91% (National Research Council, 2002). However, none of the research reviewed in the National Academy report examined the accuracy of polygraphy when used in post-conviction or therapeutic contexts. We are aware of only one study that has investigated polygraph accuracy in a post-conviction setting (Kokish et al, 2005). In this research 95 sex offenders taking part in treatment groups in California and assured of anonymity were asked about the accuracy of the 333 polygraph tests they had completed. Eighteen individuals claimed to have been wrongly accused of deception on 22 tests, and 6 individuals to have been wrongly labelled as non-deceptive on 11 tests, leading the researchers to conclude overall accuracy in their programme of 90%. From the data they presented, it is not possible to calculate specificity, sensitivity or predictive values. We made use of methodology similar to that of Kokish et al (2005). Our results, indicating an accuracy rate of 85% in detecting truth-telling and 84% in detecting deception, are similar to the rates found in the California offenders. Although this approach depends on the uncorroborated self-report of participants with no means of comparing their accounts with actual test outcomes, the reported accuracy rates in both samples are consistent with the National Academy of Sciences estimate of polygraph accuracy. The offenders themselves also perceived the accuracy of the polygraph to fall within this range, with the majority rating it as ‘moderately’ to ‘extremely’ accurate.
Accuracy in a clinical context
Although overall accuracy appears good, interpreting this in respect of
specific test outcomes is not straightforward. Although the negative
predictive rate (the likelihood that the person tested is telling the truth
when the examiner concludes ‘no deception indicated’) of 97% is
very high, the positive predictive rate (the likelihood that the person is
lying when the examiner concludes ‘deception indicated’) of 48% is
much less good. This does not mean, however, that polygraph outcome in
detecting deception is no better than chance: the AUC of 0.85 suggests good
predictive accuracy, as does the finding that the deceptive individual is over
five-and-a-half times more likely to be labelled deceptive than is the
non-deceptive non-deceptive individual.
The low positive predictive value may partly reflect self-presentation biases (deceptive offenders may be more likely to claim that the polygraph was wrong when caught out and less likely to disclose having ‘beaten’ it), but more relevant is the relatively low base rate of deception reported by the sample, with this admitted in only 38 of 263 tests (14%). The importance of the base rate of deception in the group of people being tested was highlighted in the National Academy of Sciences review, who observed that where base rates of deception are low, even a highly accurate test will produce more false than true positives (National Research Council, 2002). It is one of the primary reasons the review did not support the use of polygraphy in security contexts, where the base rate of deception is likely to be low (one hopes there are few spies in federal agencies); the review suggested that polygraphy only becomes viable when the base rate of deception exceeds 10%. Even based on self-report, it would appear that a deception rate of over 10% is likely to be the case within sex offender treatment programmes. However, it should also be noted that in post-conviction testing the emphasis is less on ‘passing’ or ‘failing’ the polygraph, and more on the facilitation of disclosures relevant to supervision and treatment. Getting it ‘wrong’ in a post-conviction test is of much less consequence than a wrong result in a criminal investigation or a security screen, where much more reliance may be placed on the examination.
False positives, false negatives, disclosures and false disclosures
None of the variables we tested distinguished offenders more likely to have
false positive or false negative results. Waid et al
(1979) suggested that
socialisation may be associated with false negative errors. Although
socialisation has been related to the neuroticism and conscientiousness
domains of the NEO (Costa & McCrae,
1992), neither of these characteristics distinguished false
negatives from true negatives or true positives in our study. Conversely, in
the context of a polygraph examination some individuals may feel pressured to
make untrue admissions. Nine per cent of the offenders in our study, and 5% in
the study by Kokish et al
(2005), claimed to have done
so, suggesting that although the incidence of this is not high, it is of
relevance. We found that high neuroticism and low conscientiousness scores
characterised those who reported making false admissions; the former is
associated with pervasive feelings of guilt, fear and embarrassment as well as
high impulsivity, and the latter with being less scrupulous and reliable. This
suggests that individuals who falsely disclose may be more emotionally
disturbed in general, and more impulsive; in difficult interview situations,
they may cope by ‘confessing’. Six of those who reported making
false disclosures in our study attributed this to either a fear of getting
into trouble with their probation officers or feeling pressured by the
polygraph examiner.
In summary, our findings support the view that post-conviction polygraph testing is a useful adjunct to the treatment and supervision of sex offenders in the community. Accuracy rates as reported by offenders who have undergone polygraph examination appear to be of a sufficiently high level to maintain the utility value of the tests.
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Clinical Implications and Limitations |
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TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
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LIMITATIONS
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ACKNOWLEDGMENTS |
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TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMETHODRESULTSDISCUSSIONClinical Implications and...ACKNOWLEDGMENTSREFERENCES |
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Blasingame, G. D. (1998) Suggested clinical uses of polygraphy in community-based sexual offender treatment programs. Sexual Abuse: A Journal of Research and Treatment, 10, 37 –45.[CrossRef]
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Cross, T. P. & Saxe, L. (2001) Polygraph
testing and sexual abuse: the lure of the magic lasso. Child
Maltreatment, 6, 195
–206.
Emerick, R. L. & Dutton, W. A. (1993) The effect of polygraphy on the self report of adolescent sex offenders: implications for risk assessment. Annals of Sex Research, 6, 83 –103.
English, K., Jones, L., Patrick, D., et al (2000) We need you to become experts in the post-conviction polygraph. Polygraph, 29, 44 –62.
Furedy, J. J. (1996) The North American polygraph and psychophysiology: disinterested, uninterested and interested perspectives. International Journal of Psychophysiology, 21, 97 –105.[CrossRef][Medline]
Grubin, D., Madsen, L., Parsons, S., et al (2004) A prospective study of the impact of polygraphy on high-risk behaviors in adult sex offenders. Sexual Abuse: A Journal of Research and Treatment, 16, 209 –222.[CrossRef]
Hanson, R. K. & Thornton, D. (2000) Improving risk assessments for sex offenders: a comparison of three actuarial scales. Law and Human Behavior, 24, 119 –136.[CrossRef][Medline]
Harrison, J. S. & Kirkpatrick, B. (2000) Polygraph testing and behavioral change with sex offenders in an outpatient setting: an exploratory study. Polygraph, 29, 20 –25.
Hindman, J. & Peters, J. M. (2001) Polygraph testing leads to better understanding adult and juvenile sex offenders. Federal Probation, 65, 8 –15.
Kokish, R., Levenson, J. S. & Blasingame, G. D. (2005) Post-conviction sex offender polygraph examination: client-reported perceptions of utility and accuracy. Sexual Abuse: A Journal of Research and Treatment, 17, 211 –221.[CrossRef]
Lykken, D. T. (1998) A Tremor in the Blood: Uses and Abuses of the Lie Detector. New York: Plenum Press.
Madsen, L., Parsons, S. & Grubin, D. (2004) A preliminary study of the contribution of periodic polygraph testing to the treatment and supervision of sex offenders. Journal of Forensic Psychiatry and Psychology, 15, 682 –695.[CrossRef]
National Research Council (2002) The Polygraph and Lie Detection. Washington, DC: National Academies Press.
Nelson, H. E. & Willison, J. (1991) National Adult Reading Test (NART): Test Manual (2nd edn). Windsor: NFER–Nelson.
Waid, W. M., Orne, M. T. & Wilson, S. K. (1979) Effects of level of socialization on electrodermal detection of deception. Psychophysiology, 16, 15 –22.[Medline]
Received for publication January 17, 2005. Revision received June 20, 2005. Accepted for publication September 1, 2005.
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
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