Use of DNA testing in police investigative work for increasing offender identification, arrest, conviction and case clearance

The use of DNA testing as part of police investigative work has increased substantially since its emergence in the 1980s. The objective of this Campbell systematic review has been to synthesize the existing evidence on the effectiveness of DNA testing as part of routine police investigative practices compared to other more traditional forms of investigation. We have identified five studies that clearly addressed the effectiveness of DNA testing as part of a criminal investigation to improve criminal justice system outcomes. The evidence suggests that DNA testing has positive value when used to investigate a broad range of crime types. There are caveats. Other than a methodologically sound evaluation in five U.S. jurisdictions, the evidence of the utility of DNA testing for serious violent crimes is based on studies with clear methodological weaknesses. Synopsis The use of DNA testing as part of police investigative work has increased substantially since its emergence in the 1980s. The objective of this review has been to synthesize the existing evidence on the effectiveness of DNA testing as part of routine police investigative practices compared to other more traditional forms of investigation. We have identified five studies that clearly addressed the effectiveness of DNA testing as part of a criminal investigation to improve criminal justice system outcomes. The evidence suggests that DNA testing has positive value when used to investigate a broad range of crime types. There are caveats. Other than a methodologically sound evaluation in five U.S. jurisdictions, the evidence of the utility of DNA testing for serious violent crimes is based on studies with clear methodological weaknesses. Abstract BACKGROUND The use of DNA testing as part of police investigative work has increased substantially since its emergence in the 1980s. Initially used primarily in serious cases, such as homicides and rapes, recent use has expanded to include additional crimes, such as property offenses. The science behind the accuracy of DNA testing is substantial. With the growth of DNA databases, the possibility of comparing DNA evidence collected from a crime scene against a DNA database to identify suspects has become feasible. An important empirical question is whether wide scale use of DNA testing as part of routine police investigative practices will improve case outcomes. OBJECTIVES The objective of this review has been to synthesize existing evidence on the effectiveness of DNA testing as part of routine police investigative practices compared to other more traditional forms of investigation. SEARCH CRITERIA We were inclusive with respect to research design, including both experimental RCT designs and observational or quasi‐experimental studies. All studies must have provided an estimate of the effect of DNA testing (yes/no or degree of) as part of the investigative phase of a criminal case on a criminal justice system outcome, such as the identification of a suspect or a conviction. SELECTION STRATEGY We searched 35 electronic databases and reviewed the references of seminal works in the area. This produced more than 10,000 titles that we scanned for potentially eligible works. These potentially eligible works were examined more carefully and evaluated against our eligibility criteria. This process resulted in five studies that met our inclusion criteria. Four of these five studies were dissertations or government reports. DATA COLLECTION AND ANALYSIS Studies were coded with respect to a range of methodological and substantive features. When possible, odds‐ratios were computed to reflect the effect of DNA testing on criminal justice system outcomes. Given the diversity of designs, we did not meta‐analyze results across studies. We did, however, use meta‐analysis to synthesize results across multiple sites within two of the five studies. MAIN RESULTS Across studies we found generally positive results regarding the utility of DNA testing. The results from the single experimental study on the effectiveness of DNA for property crimes were consistently positive across the included sites. A time‐series analysis found a relationship between the size of a local DNA database and clearance rates for most crime types. Two of the remaining three quasi‐experimental designs found positive, and sometimes large, effects for the benefits of DNA testing. A study of homicides found a negative effect of the value of DNA. Clear alternative explanations for this finding are plausible. REVIEWERS' CONCLUSIONS The evidence suggests that DNA testing has value when used to investigate a broad range of crime types. There are caveats to this conclusion, and additional high quality evaluations are needed to establish the robustness and generalizability of these findings. Other than a methodologically sound evaluation in five U.S. jurisdictions, the evidence of the utility of DNA testing in investigative practices for serious violent crimes is based on studies with clear methodological weaknesses.