Recent studies suggest that the reported effect sizes of prevention and intervention trials in criminology are considerably larger when program developers are involved in a study than when trials are conducted by independent researchers. This paper argues that the possibility of these differences may be due to systematic bias related to conflict of interest. If this is true, the results could be (1) the inability to estimate the true effect of interventions unless the approximate effect size of bias is known, (2) public trust in the research program of evidence-based prevention would be undermined, (3) systematic bias directs research resources into areas that may have less promise than others where bias is less common, and (4) an incentive for new researchers to adopt the same problematic practices that exist in the field is created. A review of the evidence shows that the possibility of a substantial problem cannot be currently rejected. In recognition of these dangers, significant efforts have been made over the past decade to improve standards for conducting and publishing experimental and quasi-experimental studies in many domains of research on evidence-based prevention and intervention. Figure, tables, and references