Exploring Some Analytical Characteristics of Finite Mixture Models

Finite mixture models have become increasingly prevalent in criminology over the past two decades. Yet there is no consensus about the appropriate criterion for model selection with finite mixture specifications. In this paper, we use simulation evidence to examine model selection criteria. Our focus is on mixture models for event count data like those often encountered in criminology. We use two indices to measure model selection performance. First, we examine how often each criterion chooses the correct specification. Then, we investigate how closely the finite mixture models selected by these criteria approximate the true mixing distribution used to simulate the event count data. We consider three sets of simulations. In the first set, the underlying model is itself a three component Poisson-based finite mixture model. In the two other sets of simulations, the underlying distribution of the Poisson rate parameter follows a continuous distribution. The analysis shows that both AIC and BIC perform well under certain sets of circumstances likely to be encountered by criminologists.

The relationship between trauma and violence in a jail inmate sample

Research suggests there is a link between trauma and violence, although the nature of the relationship is rather equivocal. This study explored this relationship by examining self-reported trauma as a predictor of self-reported violence in 93 jail inmates. Ninety-six percent of the sample reported experiencing a traumatic event, and 67% reported having been violent during the year preceding incarceration. Inmates reporting trauma were more than twice as likely to report having been violent than nonviolent. Stepwise multiple regression analyses suggested traumatic events, as a combined model, significantly contributed to violence perpetration. In addition, witnessing serious violence predicted perpetration of violence. Implications and limitations of the present study are discussed.     

Microchip-based cell lysis and DNA extraction from sperm cells for application to forensic analysis

The current backlog of casework is among the most significant challenges facing crime laboratories at this time. While the development of next-generation microchip-based technology for expedited forensic casework analysis offers one solution to this problem, this will require the adaptation of manual, large-volume, benchtop chemistry to small volume microfluidic devices. Analysis of evidentiary materials from rape kits where semen or sperm cells are commonly found represents a unique set of challenges for on-chip cell lysis and DNA extraction that must be addressed for successful application. The work presented here details the development of a microdevice capable of DNA extraction directly from sperm cells for application to the analysis of sexual assault evidence. A variety of chemical lysing agents are assessed for inclusion in the extraction protocol and a method for DNA purification from sperm cells is described. Suitability of the extracted DNA for short tandem repeat (STR) analysis is assessed and genetic profiles shown. Finally, on-chip cell lysis methods are evaluated, with results from fluorescence visualization of cell rupture and DNA extraction from an integrated cell lysis and purification with subsequent STR amplification presented. A method for on-chip cell lysis and DNA purification is described, with considerations toward inclusion in an integrated microdevice capable of both differential cell sorting and DNA extraction. The results of this work demonstrate the feasibility of incorporating microchip-based cell lysis and DNA extraction into forensic casework analysis.     

Relationships between concentrations of cocaine and its hydrolysates in peripheral blood, heart blood, vitreous humor and urine

Cocaine is known to degrade in vivo and in vitro by several hydrolytic mechanisms. A previous study found that the initial amount of cocaine added to plasma could be accounted for by summing the molar concentrations of cocaine's hydrolysis products and the cocaine remaining after hydrolysis. The present study was undertaken to investigate whether or not relationships might exist between such molar concentration sums for different postmortem bodily fluids. Determinations of cocaine, benzoylecgonine, ecgonine methyl ester, and ecgonine were performed using liquid chromatography/mass spectrometry (LC/MS/MS) with heart blood, femoral blood, vitreous humor (VH), and urine (UR). The results demonstrate a strong correlation between blood and VH concentrations (correlation coefficients of 0.88-0.94), weak correlation between the UR and blood concentrations (correlation coefficients of 0.61-0.64), and weak correlation between UR and VH concentrations (correlation coefficient of 0.59). The results demonstrate that ecgonine is a significant hydrolysate with concentrations on the same order of magnitude as benzoylecgonine. The results are consistent with rapid distribution of the parent drug and its hydrolysates in the blood and VH. The strong correlation between the blood and VH demonstrates that VH is an important medium for toxicology testing when attempting to make a determination of cocaine intoxication.     

Gender disparity in criminal offenses among persons of high IQ

Criminologists have largely neglected deviance among those with high IQs. This work uses Towers's (1988) concept of conventional genius to analyze how deviant behavior varies by gender among genius offenders. Like Bisi (2002), the authors expect female patterns of deviance to be lower than that for males even within this genius sample. Their work finds that male geniuses are significantly more likely to self-report ever having committed violent felonies. Among the authors' conventional genius sample of university students, gender differences in nonviolent felonies, misdemeanor offenses, and unethical behaviors are not significantly different between the female and male respondents.     

Changing patterns of addiction and public aid receipt: tracking the unintended consequences of welfare reform

Sharp declines in welfare rolls since the passage of welfare reform legislation have led many to label it a social policy success. Using data from prereform and postreform samples of welfare applicants and recipients, as well as ethnographic data on welfare reform implementation, we examine three hypotheses based on concerns raised during the welfare reform debate about the possible effects of new policies on substance abusers and addicts: First, they would be "scared off," or discouraged from applying to aid by welfare's new requirements surrounding work and treatment. Second, they might be "weeded out," or face discrimination in the application process because of concerns about the difficulty of moving them successfully from welfare to work. Third, they might be "bumped down," or shifted to local aid programs rather than moving from welfare to self-sufficiency. Our empirical analysis finds no evidence of scaring off or weeding out, and some evidence of bumping down. Using ethnographic data, we offer some possible explanations for these findings by placing them in the context of policy change and implementation in the years following welfare reform.