A cost-effectiveness analysis of the number of samples to collect and test from a sexual assault

Abstract

<jats:p>Although the backlog of untested sexual assault kits in the United States is starting to be addressed, many municipalities are opting for selective testing of samples within a kit, where only the most probative samples are tested. We use data from the San Francisco Police Department Criminalistics Laboratory, which tests all samples but also collects information on the samples flagged by sexual assault forensic examiners as most probative, to build a standard machine learning model that predicts (based on covariates gleaned from sexual assault kit questionnaires) which samples are most probative. This model is embedded within an optimization framework that selects which samples to test from each kit to maximize the Combined DNA Index System (CODIS) yield (i.e., the number of kits that generate at least one DNA profile for the criminal DNA database) subject to a budget constraint. Our analysis predicts that, relative to a policy that tests only the samples deemed probative by the sexual assault forensic examiners, the proposed policy increases the CODIS yield by 45.4% without increasing the cost. Full testing of all samples has a slightly lower cost-effectiveness than the selective policy based on forensic examiners, but more than doubles the yield. In over half of the sexual assaults, a sample was not collected during the forensic medical exam from the body location deemed most probative by the machine learning model. Our results suggest that electronic forensic records coupled with machine learning and optimization models could enhance the effectiveness of criminal investigations of sexual assaults.</jats:p>

The case for “investigate all”: Assessing the cost‐effectiveness of investigating no CODIS hit cases in a sexual assault kit initiative

“…The incremental cost‐effectiveness analyses showed that investigating all cases instead of only those with CODIS hits meant paying $9121 p/additional indictment and $12,000 p/additional conviction. Given the $241,960 tangible and intangible societal cost for each sexual assault, this is a relatively small price for the system to expend to get dangerous sexual offenders [40] off the streets, give justice to victims [43], and make the community safer [40].…”

“…From a total societal cost perspective, investigating all cases led to a cost savings of $26.48 million. Investigations with CODIS hits were more cost‐effective than those without CODIS hits [43], as a larger percentage resulted in indictments and convictions. However, also investigating cases without CODIS hits was cost‐effective due to the cost savings from future sexual assaults averted, thereby providing strong support for the “investigate all” policy.…”

Forensic intelligence: Data analytics as the bridge between forensic science and investigation

“…They call for further collection of cost data to be able to assess the value and associated ROI from probative use of forensic evidence. Since that call, several sources of cost and benefit data have emerged that will permit the ROI determination [ 15 , 17 , 22 , 23 , [41] , [42] , [43] , [44] ].…”

“…Can we determine the impact of forensic science on the justice system? Many studies have addressed the question of the value of forensic science and the measurement of those contributions ([ [1] , [2] , [3] , [4] , [5] , [6] , [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] ]). A fundamental component of that question involves what specific analytical outcomes signify value and how to measure each interpretation of value.…”

Evidentiary discrepancies in sexual assault casework within the US

“…The SAK used by trained medical or forensic professionals provides all the tools necessary to safely collect and gather evidence following a sexual assault. Although the kit contents can vary between Forensic sciences; forensic toxicology; drug-facilitated; sexual assault; DFSA; chemical submission; SANE; SART REVIEW jurisdictions and municipalities [1], they typically include instructions for collection, swabs for DNA, vials for blood collection, sterile jars for urine collection, labels for evidence, bags for storage, and documentation to initiate a chain of custody [6,7]. With respect to forensic toxicology, the results of the analyses performed on collected biological specimens do not necessarily "solve" a case, but they can support the perceived credibility of the survivor [8].…”