How accurate is polygraph over other techniques?

HOW ACCURATE IS POLYGRAPH & LIE DETECTOR TESTS OVER OTHER TECHNIQUES?

Over the past 25 years as a polygraph examiner, I’ve interviewed and polygraph tested over 11,000 people from all walks of life.

I have been trusted with my clients’ innermost secrets and with providing them with a level of truth and closure that they could not have received by any other means. The only way they’ve achieved this is through the accuracy and validity of the polygraph. I have seen many issues being resolved, as well as  relationships being restored and rebuilt as a result of the polygraph’s accuracy.

Many Innocent examinees were able to prove their truthfulness when no one wanted to believe them. Just as many examinees have finally admitted their guilt after being exposed by the polygraph test.  

 

Socially speaking, about two-thirds of examinees are typically found to be truthful during polygraph tests. This is significant, especially when an accused individual has no other means of proving their innocence. 

 

Most people think that the polygraph is not accurate and that they are easily manipulated. As an expert on the subject, this is not the case.  A comprehensive study on the Validity and Reliability of Detection of Deception conducted by D.C. Raskin, G.H. Barland, and J.A. Podlesny (1978) for the National Institute of Law Enforcement and Criminal Justice that included field studies and laboratory experiments concluded that, depending on the optimal score threshold, the polygraph is up to 98 percent accurate.

Likewise, subjects trying to “beat” the test through deception or external methods will not be able to accomplish their goal when the test is conducted by an experienced and accredited polygraph examiner.

Polygraphs have been maligned as a court-admissible forensic (investigation) tool for many years – and without good reason.

Many people will say that DNA, fingerprinting and eyewitness statements are the most accurate forensic tools that we can use in our quest for the truth.

Some will say the polygraph is not nearly as reliable as these methods. I am here to tell you the opposite.

The polygraph is the most reliable and efficient forensic tool that we can use to determine the truth.

Compared to other forensic tools, the polygraph is just as or even more accurate at determining truth or deception than any other forensic technique. 

In the following section we will take a look at how accurate the polygraph is in comparison with other forensic tools using real world data.

The data here is not here to “debunk” or discredit specific diagnostic tools or methods. As humans, we are imperfect, and can and will make mistakes. It’s important to understand that, at least in theory, all forensic tools can achieve 100% accuracy. It is the human factor that introduces errors and biases that diminish the accuracy of other techniques. 

 

Is polygraph more accurate than fingerprint evidence?

Latent, or left-behind fingerprint evidence at crime scenes is often cited as the “gold standard” of determining guilt or innocence – especially when it comes to television. 

The American Society of Crime Laboratory Directors (ASCLD) Proficiency Advisory Committee reached out to the International Association for Identification in 1994 for assistance in creating and reviewing testing materials for latent fingerprint examiners. The IAI then contracted with the Collaborative Testing Services to administer and design the external proficiency test used by ASCLD. The test includes latent prints and 10-print cards, with examiners required to identify or eliminate prints. Results from the seven years between 1995 and 2001 have shown that fingerprint evidence examiners can make an incorrect identification as high as 20% of the time and miss identifying a suspect as high as 81% of the time.

 

Year of Test	Number of Examiners	All Correct Responses %	One or more Erroneous ID %	One or more Missed ID %
1995	156	44	20	36
1996	184	16	3	81
1997*	204	61	6	28
1998	219	58	6	36
1999	228	62	5	33
2000	278	91	4	5
2001	296	80	3	17

* Respondent made more than one kind of error

 

Further, fingerprint evidence is not conclusive to the guilt or innocence of a suspect. Fingerprint evidence may appear from a suspect well before the crime took place – it does establish their presence in a room or even touching a victim’s clothes prior to the crime. It does not, in isolation, prove any wrongdoing.

 

Is polygraph more accurate than DNA evidence?

If latent fingerprints are considered the “gold standard” then DNA evidence is the “diamond standard.” There is no shortage of TV detectives insisting on DNA swabs to help incriminate suspects.

In the real world, the quality and methodology of forensic DNA laboratories can vary from accurate to “inadmissible.” Cross-contamination and mix-ups of DNA can also occur, and dishonest analysts may be “covering up” their poor work. 

The Report of the Commission of Inquiry into Forensic DNA Testing in Queensland, submitted in 2022 by Commissioner Walter Sofronoff KC, provides a clear example of the importance of adhering to best practice guidelines in DNA testing. The report was commissioned to evaluate the effectiveness of the DNA testing methods, systems, and processes used in Queensland. Unfortunately, the findings were not positive. The forensic DNA laboratory was found to fall short of best practice in multiple ways, with a significant focus on speed and throughput over high-quality science. This led to deficiencies in the validation of processes and equipment, insufficient time dedicated to thorough case reviews, and limited resources for research and development. These shortcomings are especially concerning as the laboratory is responsible for serving the criminal justice system. The report even found that failure to obtain all the available evidence from samples impacted some cases, making it more challenging to secure convictions. The implications of these findings are significant, and it is crucial that action is taken to address these failings and ensure that the laboratory adheres to best practice guidelines.

Another example is, in the aftermath of the September 11 terrorist attack on New York’s World Trade Centre, 1,592 of the 2,749 victims were identified using a variety of forensic techniques. Although 23,608 families provided DNA samples, only 111 were identified through DNA – an underwhelming 4 percent.

Errors in DNA evidence have called forensics in criminal justice into disrepute. Forensic laboratories should operate with the highest standards of accuracy and accountability, using the best quality control and independent oversight. This is to prevent wrongful conviction and the miscarriage of justice.

Again, presence or absence of DNA at a crime scene does not definitively prove guilt or innocence of a subject, much like fingerprints.

 

Polygraph accuracy vs medicine

Diagnostic errors in medicine can have serious consequences for patients and recent research has shed light on the causes of these errors. According to a study, physicians tend to be overconfident in their diagnoses, and this tendency is reinforced by both intrinsic and system-level factors. The study found that in some instances, the error rate is alarming.

In a post-mortem study of 126 patients who died in intensive care (ICU), doctors who were convinced their diagnosis was correct before the patient’s death, were wrong four times out of ten.

In another post-mortem study of 67 artery blockage patients, doctors did not suspect the ultimate cause of death in 55% of the cases.

 

Pulmonary TB	Studies that have specifically focused on the diagnosis of pulmonary TB; 50% of these diagnoses were not suspected ante-mortem
Pulmonary embolism	Of 67 patients who died of pulmonary embolism, the diagnosis was not suspected clinically in 37 (55%)
Ruptured aortic aneurysm	Of 23 cases involving abdominal aneurysms, diagnosis of ruptured aneurysm was initially missed in 14 (61%); in patients presenting with chest pain, diagnosis of dissecting aneurysm of the proximal aorta was missed in 35% of cases
Subarachnoid haemorrhage	Updated review of published studies on subarachnoid haemorrhage: 30% are misdiagnosed on initial evaluation
Cancer detection	Of the 250 malignant neoplasms found at autopsy, 111 were either misdiagnosed or undiagnosed
Breast cancer	50 accredited centres agreed to review mammograms of 79 women, 45 of whom had breast cancer; the cancer would have been missed in 21%
Melanoma	Second review of 5,136 biopsy samples; diagnosis changed in 11%
Bipolar disorder	The initial diagnosis was wrong in 69% of patients with bipolar disorder and delays in establishing the correct diagnosis were common
Appendicitis	Retrospective study at 12 hospitals of patients with abdominal pain and operations for appendicitis. Of 1,026 patients who had surgery, there was no appendicitis in 110 (10.5%); of 916 patients with a final diagnosis of appendicitis, the diagnosis was missed or wrong in 170 (18.6%)
Cancer pathology	The error rate of pathologic diagnosis was 2%–9% for gynaecology cases and 5%–12% for non-gynaecology cases
Endometriosis	Digital videotapes of laparoscopies were shown to 108 gynaecologic surgeons; the inter-observer agreement regarding the number of lesions was low (18%)
Psoriatic arthritis	1 of 2 SPs with psoriatic arthritis visited 23 rheumatologists: the diagnosis was missed or wrong in 9 visits (39%)
Atrial fibrillation	Review of automated ECG interpretations read as showing atrial fibrillation: 35% of the patients were misdiagnosed by the machine, and the error was detected by the reviewing clinician only 76% of the time
Infant botulism	Study of 129 infants in California suspected of having botulism during a 5-yr period; only 50% of the cases were suspected at the time of admission

 

The study also revealed that the breakdown in clinical reasoning often occurs because the physician isn’t willing or able to reflect on their own thinking processes and critically examine their assumptions, beliefs, and conclusions. Physicians may lack knowledge, fail to gather complete and accurate information from the patient, or misinterpret test results.

In comparison to polygraph, examiners are guided by the evidence produced from the examinee’s physiological responses and the examiner’s interpretation is independent of any external variable.

 

Polygraph accuracy vs other forensic tools

Polygraph accuracy is the overall leader over other forensic tools when it comes to determining the truth or deception of a subject. In laboratory conditions, polygraph’s efficacy was 90%, with 5% incorrect, 5% inconclusive, and a 1.3% false positive rate.

Handwriting analysis yielded an 85% correct identification rate, with eyewitness testimony being accurate only 35% of the time (9.1% false positive rate) and fingerprint analysis being correct only 20% of the time.

 

Diagnostic Tool	Correct	Incorrect	Inconclusive	False Positive
Polygraph	90%	5%	5%	1.30%
Handwriting	85%	5%	10%	1.40%
Eyewitness	35%	20%	45%	9.10%
Fingerprint	20%	0%	80%	0%

 

Polygraph tests are even more accurate than some medical tests. Polygraph has a combined sensitivity (diagnosing illness/guilt) and specificity (determining negative presence/innocence) score of 0.88, with 1 being the highest. MRI came in second at 0.87, CT scans at 0.86, and X-Rays at 0.81. 

 

Diagnostic Tool	Sensitivity	Specificity	Combined	Studies (N)
Polygraph (Diagnostic)	0.92	0.83	0.88	37
MRI	0.86	0.88	0.87	17
CT	0.83	0.89	0.86	19
US	0.84	0.87	0.86	38
X-Ray	0.77	0.85	0.81	12

 

In addition, a reliability (inter-rater agreement) comparison was made and revealed the following data:

	Polygraph	Medicine	Psychology
Agreement	91%	81%	88%
No. Subjects	102	150	174

 

Why should I choose the polygraph?

Polygraph is a scientifically tested forensic tool that provides one of the highest accuracy rates for determining truth or deception about a given subject. If you suspect someone of lying, the accuracy of the polygraph will detect deception or truthfulness much more often than other methods.

It’s important to see the polygraph in relative rather than absolute terms when it comes to accuracy. As mentioned, the presence or absence of a fingerprint at a crime scene cannot incriminate someone on its own. A polygraph examination, when conducted by an accredited examiner, will usually get to the bottom of the truth.

Above all, the polygraph provides answers to those seeking them.

For example, it can prove or disprove a significant other’s infidelity – or claims to the contrary. If the accused is found to be lying, it can give the aggrieved the proof they are looking for. If the accused is found to be innocent, it can help repair trust in the relationship.

The polygraph is a powerful diagnostic and forensic tool – it can assist in proving guilt or innocence in ways other methods cannot.

Further, for most third parties such as aggrieved spouses, family, or employers with a vested interest in determining the truth, they accept the results of the examination more so than other types of evidence. When an examinee has been found to be deceptive while insisting they are truthful, most people trust the scientific test over the actual person’s testimony.

In most cases, when a polygraph determines guilt, the guilty party confesses to the act under examination – the truth has finally caught up with them.

 

If you want to get to the bottom of a dispute or lie, contact Polygraph Australia for a confidential and discreet inquiry into polygraph examinations and sessions.

 

 

 

 

 

 

 

 

 

 

 

References

Amsel, Tuvya T. ‘Comparative Review of Polygraph and Other Diagnostic Tools and Methods’ Vol. 7, 2013, No. 1 (23) pp. 25-36.

Matte, James Allan. ‘The Connection between Score Threshold, Rate of Inconclusives and Minimum Number of Charts Required for Decision of Truth or Deception’ in European Polygraph, Vol. 7, 2013, No. 1 (23) pp. 5-11.

Commissions of Inquiry Order (No. 3) 2022, the Report of the Commission of Inquiry into Forensic DNA Testing in Queensland.