An investigation of social class inequalities in general cognitive ability in two British birth cohorts

The ‘Flynn effect’ describes the substantial and long‐standing increase in average cognitive ability test scores, which has been observed in numerous psychological studies. Flynn makes an appeal for researchers to move beyond psychology's standard disciplinary boundaries and to consider sociological contexts, in order to develop a more comprehensive understanding of cognitive inequalities. In this article we respond to this appeal and investigate social class inequalities in general cognitive ability test scores over time. We analyse data from the National Child Development Study (1958) and the British Cohort Study (1970). These two British birth cohorts are suitable nationally representative large‐scale data resources for studying inequalities in general cognitive ability. We observe a large parental social class effect, net of parental education and gender in both cohorts. The overall finding is that large social class divisions in cognitive ability can be observed when children are still at primary school, and similar patterns are observed in each cohort. Notably, pupils with fathers at the lower end of the class structure are at a distinct disadvantage. This is a disturbing finding and it is especially important because cognitive ability is known to influence individuals later in the lifecourse.     

The versatility of multi-state models for the analysis of longitudinal data with unobservable features

Multi-state models provide a convenient statistical framework for a wide variety of medical applications characterized by multiple events and longitudinal data. We illustrate this through four examples. The potential value of the incorporation of unobserved or partially observed states is highlighted. In addition, joint modelling of multiple processes is illustrated with application to potentially informative loss to follow-up, mis-measured or missclassified data and causal inference.     

Leukemia Risk Associated with Benzene Exposure in the Pliofilm Cohort: I. Mortality Update and Exposure Distribution

The National Institute of Occupational Safety and Health (NIOSH) recently completed a vital status update adding 6 years of observation on the rubber workers known as the Pliofilm cohort. Using traditional standardized mortality ratio (SMR) analysis, we investigate the impact of the additional information gathered in the NIOSH update. We also compare the effect of using three sets of job-, plant-, and year-specific exposure estimates on the evaluation of benzene's leukemogenicity. The lack of any additional cases of multiple myeloma does not support trends toward elevated risks for this endpoint (as had been observed earlier), and there is no indication of increased incidences of solid tumors (as predicted by animal studies). Qualitatively, which exposure estimates are used does not alter the conclusions. The data added in the update did not greatly modify the estimated relative risk of leukemia associated with benzene exposure, but did confirm previous findings that occupational exposure to high concentrations had leukemogenic potential. The fact that leukemia has not been observed in any individual who started employment in Pliofilm production after 1950 suggests that the observed leukemia cases could be a response to very high levels of benzene exposure that occurred during the early years of this manufacturing process.     

Coloured South Africans: a middleman minority of another kind

Beginning in the 1940s, a literature on middleman minorities emerged to demystify the intermediary economic niche that Jews had occupied in medieval Europe. They were viewed as ethnic entrepreneurs occupying the economic status gap. In the 1960s, scholars began to systematically apply middleman minority theory to colonial societies and to American society. South Africa also has classic middleman minorities: immigrants from South Asia. This article identifies Coloured South Africans as a middleman minority of another type: semi-privileged proletarians. It also offers a typology contrasting ethnic entrepreneurs to semi-privileged proletarians.     

Mixture models in survival analysis: Are they worth the risk?

There has been a recurring interest in models for survival data which hypothesize subpopulations of individuals highly susceptible to some type of adverse event. Other individuals are assumed to be at much less risk. Most commonly, in clinical trials, these models attempt to estimate the fraction of patients cured of disease. The use of such models is examined, and the likelihood function is advocated as an informative inference tool.     

Partially hidden multi-state modelling of a prolonged disease state defined by a composite outcome

Lifetime Data Analysis - For rheumatic diseases, Minimal Disease Activity (MDA) is usually defined as a composite outcome which is a function of several individual outcomes describing symptoms or...     

Spatial variability of epibiotic assemblages on marina pontoons in Singapore

Berthing pontoons, one of the most ubiquitous structures in marinas, are known to provide recruitment substrate for a variety of marine biota but little has been reported on their capacity to support epibiotic organisms in tropical marinas, and even less is known about the factors that shape their distribution in such environments. We surveyed the epibiotic assemblages on the sides of pontoons in three Singapore marinas and examined the environmental conditions that influenced their distribution. A total of 94 taxa were recorded, with each marina hosting 43–65 taxa. Assemblages among marinas were highly distinct, and, key discriminants included components of biotic (alcyonarians, hexacorallians, bivalves, and annelids), as well as abiotic (sediment, bare area and shell fragments) origin. While the assemblage variation among marinas was influenced by local environmental conditions (e.g. water motion and sedimentation rate) and pontoon material, the variation in distribution within each marina was best explained by the distance of the pontoons from the marina’s entrance (epibiotic diversity and taxa richness were lower away from the marina entrance). Knowledge on the distribution of epibiotic assemblages on pontoons is essential to identify the factors that contribute to spatial variation and encourage the design and construction of ecologically-friendly marinas. Our findings suggest that improvements to pontoon design and layout would help to augment marina biodiversity, enhance the ecology of urbanised coasts, and mitigate development impacts.     

Urban American Indian/Alaskan Natives compared to non-Indians in out-of-home care

Historically, American Indian/Alaskan Native (AI/AN) children have been disproportionately represented in the foster care system. In this study, nationally representative child welfare data from October 1999 was used to compare urban AI/AN children to non-Indian children placed into out-of-home care. Compared to non-Indian children, urban AI/AN children were older, were more often male, came from poorer homes, and were more frequently placed into group homes/ residential placements. Urban AI/AN caregivers had a greater prevalence of alcohol abuse and mental health problems compared with non-Indian caregivers.