STR analysis of artificially degraded DNA-results of a collaborative European exercise

Degradation of human DNA extracted from forensic stains is, in most cases, the result of a natural process due to the exposure of the stain samples to the environment. Experiences with degraded DNA from casework samples show that every sample may exhibit different properties in this respect, and that it is difficult to systematically assess the performance of routinely used typing systems for the analysis of degraded DNA samples. Using a batch of artificially degraded DNA with an average fragment size of approx. 200 bp a collaborative exercise was carried out among 38 forensic laboratories from 17 European countries. The results were assessed according to correct allele detection, peak height and balance as well as the occurrence of artefacts. A number of common problems were identified based on these results such as strong peak imbalance in heterozygous genotypes for the larger short tandem repeat (STR) fragments after increased PCR cycle numbers, artefact signals and allelic drop-out. Based on the observations, strategies are discussed to overcome these problems. The strategies include careful balancing of the amount of template DNA and the PCR cycle numbers, the reaction volume and the amount of Taq polymerase. Furthermore, a careful evaluation of the results of the fragment analysis and of automated allele calling is necessary to identify the correct alleles and avoid artefacts.     

Sexual and nonsexual offenders with intellectual and learning disabilities: a comparison of characteristics, referral patterns, and outcome

This article reports an evaluation of a community intellectual disability offender service over the period from 1990 to 2001. Men who committed sex offenses or sexually abusive incidents (n = 106) and men who committed other types of offenses and serious incidents (n = 78) are compared on personal characteristics, referral sources, forensic details, and outcome up to 7 years after referral. The cohorts are older than one would expect from the criminology literature, and, at about 33%, the incidence of mental illness is consistent with some previous studies. A greater proportion of sex offenders had criminal justice involvement and a formal disposal from court. Fire raising was not overly represented as an offense. There was a higher rate of reoffending in the nonsexual cohort, which persisted up to 7 years. Investigating only reoffenders, there was a considerable amount of harm reduction recorded up to 7 years, statistically significant up to 5 years following initial referral.     

An Estimator for Some Binary-Outcome Selection Models Without Exclusion Restrictions

This article provides a new maximum-likelihood estimator forselection models with dichotomous dependent variables when identicalfactors affect the selection equation and the equation of interest.Such situations arise naturally in game-theoretic models whereselection is typically nonrandom and identical explanatory variablesinfluence all decisions under investigation. When identicalexplanatory variables influence selection and a subsequent outcomeof interest, the commonly used Heckman-type estimators identifyfrom distributional assumptions about the residuals alone. Whenits own identifying assumption is reasonable, the new estimatorallows the researcher to avoid the painful choice between identifyingfrom distributional assumptions alone and adding a theoreticallyunjustified variable to the selection equation in a mistakenattempt to "boost" identification. The article uses Monte Carlomethods to compare the small-sample properties of the estimatorwith those of the Heckman-type estimator and ordinary probit.     

Contraceptive behavior in adolescence: A decision-making perspective

The contraceptive behavior of adolescent girls was viewed from a decision-making perspective. A semistructured interview protocol was used in interviewing 120 girls aged 12–19 in three clinics (Teen Family Planning, Prenatal, Pediatric Acute Care) at Michael Reese Hospital and Medical Center on (1) demographic in formation; (2) sexual and obstetric history; (3) contraceptive and sexual knowledge, attitudes, and practices; (4) environmental pressures; (5) personality factors; and (6) decision-making style. We found that the girls were generally poor contraceptors. They viewed the costs of contraception (in terms of safety) to be high; and they positively valued physical intimacy, opportunities for which come up unexpectedly and sporadically. These factors, along with their ambivalent views toward pregnancy and childbearing seemed to encourage their risk-taking behavior. Once pregnancy occurred, it was carried to term because of the strong internal and external pressures they felt to have and keep the baby. The peer-led intervention program that we are developing based on the survey findings will focus on (1) the teenagers' lack of accurate and complete knowledge about birth control and conception, (2) their limited sense of options concerning birth control and pregnancy outcomes, and (3) their poor understanding of and lack of insight into what motivates their behavior.This study is part of the investigation being conducted by the YADMAC (Young Adult and Adolescent Decision Making About Contraception) Project at Michael Reese Hospital and Medical Center, 2959 South Cottage Grove, Chicago, Illinois 60616. The authors are all members of the YADMAC research team.Received Ph.D. from the University of Chicago. Current interests are human sexuality and reproductive behavior. Currently at Department of Psychology, St. Xavier College.Received M.D. from the University of Michigan. Current interests are liaison child psychiatry and adolescent sexuality.Received Ph.D. from the University of Chicago. Current interests are early adolescent development issues.Current interests are puberty and sex differences.B. A. candidate in social work, Roosevelt University. Current interests are adolescent sexuality and contraceptive behavior.