The Caddy Review

Caddy Review - an update following the judgement in Reed

• As regards the necessity to quantify the amount of DNA, the Review was primarily concerned to avoid the phenomenon of overamplification (i.e. too much DNA) . The Review states, “Other forensic science providers routinely quantify the DNA extract believing that in so doing it reduces the chances of generating over amplification of the PCR products, something the review has observed with some FSS analyses. Additionally these providers believe that this enables a better estimate of potential inhibition. Unless there is a recognised method for addressing problems relating to over amplification, the reviewers would favour this second approach.” Professor Jamieson’s concern was the necessity to measure the amount of DNA to know how little was there in order to provide a rational method for accounting for the expected stochastic effects with such low amounts. It is this reason that the Appeal Court in Reed appears to have recognised, and accepted that it is necessary to quantify the amount of DNA to verify that it is above that level where stochastic effects may compromise the interpretation. This, in essence, has been Professor Jamieson’s position from the very first assessment of the LCN technique: “We believe that it is impossible to assess the probative value of LCN profiles because of the lower the amount of DNA, the greater the error (drop-in, drop-out, peak height imbalance, large stutter peaks), yet by definition the amount of starting DNA in this case is unknown. Therefore, the prosecution cannot take reasoned account of the potential error in their results, thereby also eliminating the possibility of estimating their probative value (aside from the presumption that it is insufficient to be used with the conventional SGM+ method).” [From statement of Prof Jamieson made to Omagh Bombing trial]

• For the avoidance of doubt: in our opinion it is the presence of stochastic effects that affect the reliability of a DNA profile, not the amount of DNA or the method used.

• The judgement in that trial has been widely quoted, including by the Caddy Review, in stating the purpose of validation. That purpose, stated verbatim by WeirJ and endorsed by the Review, was supplied to the Court in Professor Jamieson’s statement and is abstracted from the US SWGDAM standards.

• The most recent Appeal Court decision would appear to endorse Professor Jamieson’s reservations about the limitations of the LCN technique.