Is there a need
to enhance jurors’ understanding of forensic issues?


   With an increased number of violent crime in
recent years, forensic science plays a more significant role in the
investigation of the case. In a field of forensic science, case investigation
involves drawing scientific discipline of different areas such as physics,
biology and mathematics. As techniques and apparatus used in case assessment
and interpretation become more developed, the science and theories behind can
be more complicate to understand. Therefore, it is vital that forensic experts
present their findings, either orally in court room or via a written report, in
an approachable manner such that the jury can comprehend more easily without
misconception. In United Kingdom, trials are held
using the adversarial system in which jurors are 12 lay member of public chosen
randomly; jury selection is regulated by the Section 321 of Schedule 33 of
Criminal Justice Act 20031. They
come from different background and vary in experience and academic
qualification. They are selected to consider evidence presented in trial to
determine whether the defendant is guilty of charge or not. Due to complicity
in science applied in case assessment and interpretation, concern about if
jurors need to improve their understanding of forensic issues in order to interpret
the case fully and make corresponding decision has been raised. As such, it is
essential to consider and balance between the pros and cons of enhancing
jurors’ knowledge in forensic science.

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   Considering the advantages of improving
jurors’ understanding of forensic issue, it is first essential to understand
the problems that jury is facing with forensic reports. Taking DNA evidence as an
example, difficulties of juror interpreting DNA expert testimony and
mathematically presented probabilities have been revealed.2
Mixed DNA profile is frequently seen, for example in a case of rape, R.V. Karrar3.

It is particularly difficult to report multiple DNA because usually only victim’s
DNA profile is identified, the number and identities of other contributors
remain unknown. Incomplete DNA profile is also found, with a high risk of
contamination during transfer and analysis. These difficulties associated with
mixed DNA profile are taken into consideration when reporting a match in expert
testimony. But numerous experiments4
conducted and research5
highlight that the mock jurors fail to understand the probabilities6
and likelihood ratio7
expressed in an expert report, fall into the trap of prosecutor’s fallacy8,
and unable to comprehend the statistical calculation used in expert testimony9.

Therefore, it is important to ensure jury interpret information properly by
widening their knowledge on this aspect.

   It is desirable to provide quantifiable
outcomes to jury, as such forensic match evidence is usually given as a
numerical scale or statistical ratio. Yet, jurors’ lack of knowledge on
likelihood ratio draw our attention to this topic. It
has been reported that mock jurors think a probability match of 0.1 in 100 is
‘more likely’ than 1 in 1000, but in fact they are identical values.10 For instance, jurors can
easily be mistaken by the prosecutor’s fallacy. In R.V. Deen11
and R. V. Doheny; R. V. Adams12,
where the error of prosecutor’s fallacy was seen, the fallacy misled to judge
to sum up the case on ground of probability being nearly certain. Thus it led
to miscarriage of the case. The
Law Commission Report No. 325 proposed to reform the law ruling the
admissibility of expert evidence13. The
case R.V. Sally Clarke14 and R.V.

Angela Cannings15
were mentioned as they involved unreliable statistical evidence given by an
expert and such information were misused by the jury. Due to statistical test
and likelihood ratio are used frequently during representation of evidence at
court, it is important jury understand the probative weight of a match even in
the context of error evidence. If knowledge on statistical calculations and interpretation
of jury have been improved, this will reduce the chance of confusion and
misconception on probability match, in the other words jurors would be able to
evaluate the weight and value of a piece of evidence, resulting in less likely
of miscarriage of case and therefore misjudgment of jury.

   Another reason of improving jurors’ forensic
understanding is the CSI effect. The CSI TV programs exaggerate forensic
it has been suggested that the CSI effect has tricked people into overestimating
the accuracy and effectiveness of forensic science.17
Individuals with limited knowledge on DNA may misunderstand that a DNA match is
Studies have indicated that jury’s construction of the forensic science were affected
by TV programs.19
It is arguable that the CSI effect gives forensic evidence more weight than it
has. Jury are relying on the credibility of the expert which they think expert
is unquestionable instead of digesting the content of the evidence themselves. For instance, a statistic
probability for a coincidental DNA match is one in a billion, but juror
perceive this information as infallible, without accounting for false match and
laboratory errors.20 Some
suggested mock jurors are more dependent on incidental hint such as credibility
of expert instead of examining the evidence when the expert evidence is more
Nevertheless, if jurors are able to understand that a match is not an absolute
certain, they would be able to make their own judgment rather than relying totally
on other people’s words. It would also aid the jurors in picturing the case.

   Jury, without their own awareness and
ability to comprehend the evidence reported, could easily be misled. Other than
evidence in court, they also receive information of the case via media; they
could be bias due to victim sympathy and prejudgment on defendant.22
Moreover, passing information is also likely to provide prejudice to the
results. Therefore, independent thinking and unbiased decision making of jurors
are key and these can be reached by improvement on understanding in forensic

   With a knowledge gain of forensic evidence,
jurors would be able to understand and evaluate the forensic evidence and make
their own judgment, rather than taking expert’s words as certain. This allows
them to have a bigger insight and understanding to the case, meaning they can
be more rational and logical when facing the evidence which would greatly help
in decision making of the jury.

   Yet, there are downsides of enhancing
jurors’ understanding of forensic issue. Firstly, cost will be the major
problem. Assuming that jurors will have to attend lectures on forensic science
or they will be given background material to read before trial, the amount of
money costs in educating jurors cannot be excluded. A professional expert would
have to deliver talks or lessons on forensic issues regarding to the case; this
could add up to the fee of court or tribunal. There is also no agreement on how
much the jurors anticipate on the lectures. Even if reading materials are given
to jury instead, there is no guarantee that jurors will read and be able to
understand the material clearly. In fact, most of the jurors were
non-interactive during the DNA tutorial of mock jury.23
In this case, it will lose the point of enhancing jurors’ forensic
understanding. Moreover, it is arguable that it would not be fair if the losing
party have to pay for the education of the jury either.

   Other than cost, time is another main issue.

Currently, jury service lasts up
to 10 working days24,
the length of trial could be longer depending on the case. If the jurors need
to be educated before the trial starts, the length of trial will extend. Duration
of these sessions would also be unknown as this depends on the evidence being presented
in court. Many cases use multiple forensic evidence to secure a prosecution or
a defense. Evidence on different
specialized areas imply jurors would have to attend numerous lessons on various
topics. Jurors would have to take time off work, which leads to loss of
earning, particularly for self employed people. 450000 people perform jury duty
each year for violent crime25;
if trials are longer because of the lessons on forensic understanding, this
will have an impact on the economy of the country, even if it is small. It is
not unusual that jurors might have negative view on lessons of science as it appears
to be formal education. Longer trial with these lessons will add burden to
juror economically and mentally.

under the adversarial system used by English Law, jury is selected randomly in
order to prevent bias. Jurors are supposed to use their common sense to properly
analyze expert’s opinion evidence for evidentiary reliability, however, if all
jurors have background and knowledge on forensic science, this implies they
could overcomplicate the issue and may not be objective. This will affect the
fairness of the trial significantly as a result. Moreover, professional jury come
under the inquisitorial justice system which is not used by the English Law.

Therefore, it would be contradictory to enhance jurors’ understanding on
forensic issues. Such proposal of improving jury’s forensic knowledge would
unlikely to be practical under English Law.

   To conclude, with
a developing forensic technology nowadays, scientific knowledge behind becomes
more complex which raises an issue of whether juror can comprehend and analyze
the expert evidence in order to make determine the defendant is guilty of
charge or not. Despite the advantages of enhancing jurors’ forensic
understanding, it is deemed the major drawback of cost, time and law issue
would overcome the pros. An alternative solution to this matter is introduce
new test or evaluative system to examine if a piece of evidence brought by the
expert is admissible or not, as proposed by the Law Commission. The statutory test aims
to asses the qualification of expert and admissibility of expert evidence; expert
has to explain his hypothesis, chain of reasoning that leads to his opinion and
weakness of his conclusion, with reference to properly conducted scientific
research instead of personal experience. It is also a requirement to provide
likelihood ratio based on both prosecution and defense proposition. This reform
has been put forward to reduce risk of unreliable evidence based on invalid
hypothesis and implementation of such proposal is yet to be confirmed.


Criminal Justice Act 2003, Section 321 of Schedule 33

Goodman-Delahunty J. and Hewson L. 2010, Improving Jury Understanding and Use
of Expert DNA Evidence, Australian Institute of Criminology

3 R.V. Karrar (Bassam Abdu),
R.V. Jamil (Kamar), R. V. Dogar (Anjum Javaid), R. V. Dogar (Akhtar Javid)
2015 EWCA Crim 850

Dartnall S. and Goodman-Delahunty J, 2009, Enhancing Juror Understanding of
Probabilistic DNA Evidence, Australian Journal of Forensic Science, 38:2, pp.

85-96, DOI: 10.1080/00450610609410635

Goodman-Delahunty J. and Hewson L. 2010, Improving Jury Understanding and Use
of Expert DNA Evidence, Australian Institute of Criminology

Villejoubert G and Hlandel DR, 2002, The Inverse Fallacy: An Account of
Deviations from Bayes’ Theorem and the Additivity Principle. Mernor). &
Cognition, 30, pp. 171-178.

Koehler JJ, 1996, On Conveying the Probative Value of DNA Evidence:
Frequencies, Likelihood Ratios and Error Rates, University of Colorado Law
Review, 67, pp.859-886

Thompson WC and Schumann EL, 1987, Interpretation of statistical
evidence in criminal trials: The prosecutor’s fallacy and the defense
attorney’s fallacy. Low and Human Behavior, 11, pp. 167-187.

9 Findlay hl and Grix J, 2003, Challenging forensic evidence? Observations
on the use of DNA in certain criminal trials. Current Issues in Criminal
Justice, 14, pp. 269-282.

 Koehler J. J. and
Macchi L., 2004, Thinking about low-probability events: An exemplar-cuing
theory. Psychological Science, Vol. 15, No. 8, pp. 540-546

11 R. V. Deen CACD
21 DEC 1993

12 R v Doheny; R v Adams 1997 1 Cr. App. R. 369

13 Law Commission Report No. 325, 2011, Expert
Evidence in Criminal Proceeding in England and Wales

14 R. V. Sally Clark
2003 EWCA Crim 1020; 2003 2 F.C.R. 447; (2003) 147 S.J.L.B. 473

15 R. V. Angela
Cannings 2004 EWCA Crim 1

Cole S. and Dioso R., 2005, Law and the Lab: Do TV Shows Really Affect
How Juries Vote? Let’s Look at at the Evidence, WALL ST. J., at W13

Kimberlianne Podlas, 2006, “The CSI Effect”: Exposing the Media Myth, 16

18 Schweitzer N. J.,
2007, The CSI Effect: Popular Fiction about Forensic Science Affects the
Public’s Expectations about Real Forensic Science, 47 JURIMETRICS, pp. 357,

Robbers M. L. P., 2008, Blinded by Science: The Social Construction of Reality
in Forensic Television Shows and its Effect on Criminal Jury Trials, Criminal
Justice Policy Review, Volume 19, Issue 1, pp. 84-102

20 Koehler JJ, 1996, On
Conveying the Probative Value of DNA Evidence: Frequencies, Likelihood Ratios
and Error Rates, University of Colorado Law Review, 67,

21 Goodman-Delahunty
J. and Hewson L. 2010, Improving Jury Understanding and Use of Expert DNA
Evidence, Australian Institute of Criminology


J. and Hewson L. 2010, Improving Jury Understanding and Use of Expert DNA
Evidence, Australian Institute of Criminology

Gov.uk. (2017), Jury Service – GOV.UK online
Available at https://www.gov.uk/jury-service

2008, How is a jury selected?, BBC News,
14th January 2008, pp. 1

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