Pool Screening: An Example of Independent Nonidentical Bernoulli Trial

Pool screening is a widely used study design to make inference about the probability of a subject being positive for an infection when the probability is extremely low. When the pool sizes are unequal, outcomes of pool screening follow independent nonidentical Bernoulli distributions. This paper presents different calculation methods for the probability distribution of T, the number of positive pools. Marcus and Lopes recursive method is recommended.     

Why has the prevalence of obesity doubled?

The prevalence of obesity has doubled over the last 25 years. We estimate the effects of multiple socio-environmental factors (e.g., physical demands at work, restaurants, food prices, cigarette smoking, food stamps, and urban sprawl) on obesity using NLSY data. Then we use the Oaxaca–Blinder decomposition technique to approximate the contribution of each socio-environmental factor to the increase during this time. Many socio-environmental factors significantly affect weight, but none are able to explain a large portion of the obesity increase. Decreases in cigarette smoking consistently explains about 2–4 % of the increase in obesity and BMI. Food stamp receipt also consistently affects the measures of weight, but the small decrease in food stamp program participation during the period we examine actually dampened the increases in obesity and BMI. Collectively, the socio-environmental factors we examine never explain more than about 6.5 % of the weight increases.     

The effects of race,ethnicity, and age on obesity

About 30% of Americans are obese, which is roughly a 100% increase from 25 years ago. This study examines the effects of changes in the racial/ethnic composition and age distribution on the prevalence of obesity, identifies the portion of the increase in obesity caused by these changes, and projects the effects of future racial/ethnic and age changes on obesity using National Health and Nutrition Examination Survey data. Results indicate that racial/ethnic composition changes and age distribution changes have accounted for about 10% of the increase in obesity over the last 25 years. However, future racial/ethnic and age changes are not projected to increase obesity substantially.      

Family size and child mental disorders in Bahia,Brazil

The relationship between family size and child mental disorders was assessed through a prevalence study conducted in an urban neighborhood of Salvador, Brazil. From a representative sample of 828 children aged between 5 and 14 years, 23.3% were diagnosed as exhibiting varying degrees of mental disorders. Diagnoses were based on psychiatric interviews, following screening using the QMPI (a Portuguese-language screening questionnaire). Results supported the hypotheses that: (1) children from smaller families would exhibit higher prevalence of mental disorders than those from larger families; and (2) prevalence of neurotic and psychosomatic disorders would be lower for children from larger families than from smaller ones. Significant associations were also found between family size and diagnosis and severity of child mental disorders. Controlled analyses indicated that these relationships were not confounded by age or sex of the child, family social class, or family type.     

A new look at the marriage market and nuptiality rates, 1915–1958

The system of nuptiality probabilities for never married males and females, the “marriage regime,” is viewed as a population transformation, which operates on a population thereby changing the composition. The marriage regime has many properties common to other population transformations, but embodies a constraint such that, in general, the marriage regime cannot be strictly stable over time. The approach is applied to study the “marriage squeeze,” the alteration in marriage patterns that results from an imbalance in the “marriage market” or numbers of never married males and females at the usual marriage ages. Using data on age at first marriage for the 1960 American white population, nuptiality probabilities by single year of age and sex are estimated for the years 1915–58. Annual estimates also are made of the relative number of eligible mates (never married of the usual marriage ages) for never married persons of a given age and sex. No close correspondence is found between annual fluctuations in the marriage market and in the nuptiality probability, possibly because of the crudeness of the estimates. Alternatively, response to the imbalance may take another form such as marriage postponement or a redefinition of eligibility.