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Questionable research practices are a well-recognized problem in psychology. Coding bias, or the tendency of review studies to disproportionately cite positive findings from original research, has received comparatively little attention. Coding bias is more likely to occur when original research, such as neuroimaging, includes large numbers of effects, and is most concerning in applied contexts. We evaluated coding bias in reviews of structural magnetic resonance imaging (sMRI) studies of PCL-R psychopathy. We used PRISMA guidelines to locate all relevant original sMRI studies and reviews. The proportion of null-findings cited in reviews was significantly lower than those reported in original research, indicating coding bias. Coding bias was not affected by publication date or review design. Reviews recommending forensic applications—such as treatment amenability or reduced criminal responsibility—were no more accurate than purely theoretical reviews. Coding bias may have contributed to a perception that structural brain abnormalities in psychopaths are more consistent than they actually are, and by extension that sMRI findings are suitable for forensic application. We discuss possible sources for the pervasive coding bias we observed, and we provide recommendations to counteract this bias in review studies. Until coding bias is addressed, we argue that this literature should not inform conclusions about psychopaths' neurobiology, especially in forensic contexts. [ABSTRACT FROM AUTHOR]

Neurobiological theories of psychopathy typically include abnormalities in paralimbic circuits, and a neurobiological profile of paralimbic dysfunction in increasingly invoked in applied legal settings. The current study systematically evaluated whether sMRI and fMRI findings in PCL-R defined psychopaths suggest paralimbic dysfunction. Our review indicates diffuse and variable neural correlates of psychopathy, with numerous issues complicating the interpretation of these heterogeneous data. Our review also extends previous discussions concerning how this heterogeneity may be related to sample characteristics, methodological variations, and statistical analyses. To elucidate the neural correlates of psychopathy, researchers may need to clarify the relationship between psychopathy and co-occurring conditions (such as substance use disorders) both conceptually and methodologically. Our review also indicates that caution is warranted when introducing these data in applied contexts. [ABSTRACT FROM AUTHOR]

Though it has been argued that courts should admit biogenetic evidence on psychopathy, no research to date has evaluated whether individuals with clinical psychopathy have consistent genetic correlates. The current study: 1) systematically reviewed all quantitative and molecular genetic studies of PCL-R psychopathy, and 2) assessed the quality and reproducibility of findings. Using PRISMA guidelines, we reviewed 1 heritability and 15 molecular genetic studies of PCL-R psychopathy. Sample characteristics, research design, and the main findings of each study were qualitatively synthesized according to candidate neurotransmitter systems. We also assessed broad metrics of study quality such as sample generalizability, accounting for environmental or clinical variability in analyses, and replication of effects. Heritability estimates for the facets of clinical psychopathy were low. Molecular genetic findings were inconsistent and mostly unreplicated. Further, replicated findings were contradictory; elevated dopamine metabolite levels observed in independent samples was qualified by a lack of association between a candidate dopamine polymorphism and PCL-R scores. Inconsistent findings may be related to issues with study quality. Though most studies had clear hypotheses and generalizable samples, few accounted for clinical complexity of those samples, environmental factors, or gene-environment interplay. The current review suggests that the genetic bases of PCL-R psychopathy are not robust enough for forensic application. Genetic findings in people with antisocial characteristics (violence, addiction, CU traits) may not generalize to those with PCL-R psychopathy. Though genetic bases for psychopathy are widely accepted, we found very little evidence for consistent genetic correlates when we systematically reviewed studies of legally relevant PCL-R psychopathy. [ABSTRACT FROM AUTHOR]