Sunday, December 04, 2011

Disclosure to Defence, Opinion and Bayesian Statistics

Disclosure to Defence, Opinion  and Bayesian Statistics

The reported outcome from the trial and appeals of R v Adams ( [1996] 2 Cr App R 467, [1996] Crim LR 898, CA and R v Adams [1998] 1 Cr App R 377, The Times, 3 November 1997, CA) rulings was the Courts ousted explicit Bayesian statistics from the reasoning admissible before a jury in DNA cases. However, calculating the probabilities for say cell site analysis activity/location, partial recovery of a file's data and its likelihood to being a particular image etc using Bayesian, I do not to suggest that this case disbars individuals from using it in their analysis. Importantly, the case opens the doors of transparency in relation to revelation of previous consideration about its use for evidence, what measures the person has been taken to prevent assumptions about unproven facts implied as accurate and so on.

To assist the transparency principle, it should be understoood a fundamental tenet of forensics is the practice of open, free and frank discussion and disclosure about pitfalls, flaws or unsolved errors in practices, process or procedure should not be avoided.

To illustrate some ideas of lacking in transparency.  If an examiner uses eg machinery that is out of date or flawed in its operation, then clearly it is not the manufacturer that is at fault. The examiner applies the use of the machinery to obtain, produce or treat the evidence. The examiner, it is expected, who uses the machinery should understand the technicality and science in which they are involved and be able to determine in advance of the machinery use its capability (drawbacks/limitations) when assessed against known facts and requirements. Moreover, to warn about issues if the machinery then produces random output upon which its user then decides to opine statistics, probabilities and theorems being drawn from the output of the machinery.

To suggest two of many cases where we may apply the above illustration:

Case 1: would the occurrence of a mobile station using a particular set of Masts in a four hour period suggest the MS was within a defined area? The radio test equipment used to conduct tests would be unable to confirm if the operator uses "directed retry" as to an MS's call history, as the radio tests conducted are post event. The knowledge the user of the equipment must have is where to get that information if it cannot be obtained from the test results?   Without knowledge of directed retry to produce statistics about occurrence could amount to opining random speculation.

Case 2: IPhone is a popular smart phone. The release of iOS5 introduced 'iMessaging' - a messaging service for texts, emails etc using the cellular network or WiFi as the transport paths to communicate messages. 'iMessage' falls under the iPhone Message App which is equally shared with 'SMS text messaging' - which is only sent over the cellular network. An interesting feature with iMessage is that messenging with another iOS5 device it highlights the message in 'blue'. Moreover, where the user's iPhone uses a previous OS (iOS4 or earlier) the messages appear 'green'.  However, a further distraction from the straightforward blue/green operational scenario is where an iOS5 device communicating to another iOS5 device using iMessaging starts off in blue but then turns to green? Avoiding the issuesassociated with identity and origin, there are huge possibilties to spend hours calculating or producing statistics about the content of a message, but what happens when consideration is given to the blue/green paradox and the handset reading software tool fails to identify detect which messages are blue or green?

At the top end, using quantifying techniques like Bayes to opine a theory from which a conclusion can be drawn can be fraught with flaws in the absence of knowledge, skill and experience about the science subject matter in which the person works. The same can be applied at the other end, by avoiding those with knowledge, skills and experience for simple platitudes, dumbed down evidence or psychologically trickery (getting others to do what you want them to do) to avoid answering the question can lead to the production of a philistine opinion/conclusion.

Turning to another point about this case. A useful influence that has also been reported that arose in this case during the various hearings and appeals apparently led to both experts required  to consider the expert findings in order to respond to two fundamental questions. In order for that to be achieved "The scientist adducing the 'DNA comparisons'  should do so with his calculations of the random occurrence ration. Whenever such evidence is to be adduced, the Crown should serve the defence with details of how the calculations have been carried out, sufficient to enable the defence to scrutinise the basis of the calculations. The forensic science service should make available to a defence expert, if requested, the database upon which the calculations are based."

If we are to reflect how the need for proper and transparent disclosure and the equal treatment of the defence expert may be put into practice for calculations and databases, examples could be expressed as:

Handset and SIM/USIM Data Acquisition - complete acquired (not partially acquired) data in those devices to be disclosed to the defence; disclose report and identify standards etc and any opinion formulated

Cell Site Analysis - disclosure of radio test measurements, surveys, materials from relevant mobile network operator/s and confirmation of all material considered and disclosed (including handset/SIM report; call records; cell site etc)

Call/Billing Record Analysis - disclosure of billing, CDRs, TAP and IRA/IOT roaming records, IMSI/IMEI analysis, voice and data usage etc

As cases, like Adams, do not appear to have been overruled for upholding established principles, it would be odd to see them overlooked in times of economic cutbacks: eg " a good day to bury bad news " approach were it to be inferred or implied:

- disclosure to be costly,
- causes difficulty to those who seek to simplify evidence because they do not technically understand the evidence (and the logical and natural consequence of the latter),
- the dumbing down of evidence.

A strong supporting tenet in the doctrine of disclosure is the linked parallel requirement for appropriate and necessary experience and competence of the expert to deal with the compiling or assessment of the evidence. That is, as opposed to an inexperienced or less experienced person or a person indirectly involved in the science/technology element of the evidence being encouraged to have a stab at interpreting the evidence.  Such examples, where society would most probably find the latter notions abhorrent were they to be practiced by one party or another, and quite rightly so, can be suggested as:

a) an anesthetist assisting a brain surgeon in theatre (thus working in close proximity, similar as one may do in a company) :- should the anesthetist be asked to opine about surgically gaining access to a brain tumour or the likelihood of the success/failure of such surgery?

b) a barrister who has dealt with 40 cases of dentist mistreatment should s/he be asked what procedure is needed for removing impacted wisdom teeth or the likelihood of success/failure of removing the impacted teeth?

c) the analogies above applied to persons involved with DNA, blood sampling, fingerprinting and technology evidence etc... may equally draw opinion on a view society may take?

d) where the person being asked to give opinion has far less experience is preference over highly experienced persons? 

The discussion in this thread is not to argue or advise on law (as I am not holding out to do so), nor am I qualified in this area, nor am I suggesting seeking the advise of anyone other than those who are highly experienced in eg law. The discussion is to identify a case and expose how it can highlight unnecessary challenges placed on the standards and quality of evidence that may arise, introduced by poor opinion or opinion generated from over-confident attititude of inexperienced or less experienced individuals. 

Additional case reference: R v Doheny and Adams [1997] 1 Crim App R 369.

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