Deafness and hearing loss - a global health problem

Throughout history deafness and hearing loss have been widely misunderstood. Issues concerning the education of deaf children, appropriate means of communication and remediation of deafness have consistently been a source of heated debate between the professionals working with the deaf and the deaf people themselves. The purpose of this paper is an attempt to illustrate these issues and to impart to the reader the realization that a diagnosis of "deaf" means so much more than the inability to hear and understand speech and other sounds. It is a way of life that cannot be ignored (Jacobs, A Deaf Adult Speaks Out, Harvard University Press, Washington, DC, 1994).     

One-Hit Models of Carcinogenesis: Conservative or Not?

One-hit formulas are widely believed to be "conservative" when used to analyze carcinogenesis bioassays, in the sense that they will rarely underestimate risks of cancer at low exposures. Such formulas are generally applied to the lifetime incidence of cancer at a specific site, with risks estimated from animal data at zero dose (control), and two or more additional doses that are appreciable fractions of a maximum tolerated dose. No empirical study has demonstrated that the one-hit formula is conservative in the sense described. The Carcinogenesis Bioassay Database System contains data on 1212 separate bioassays of 308 chemical substances tested at exactly three evaluable doses. These provided sufficient data to examine 8432 specific combinations of cancer site with sex, species, and chemical. For each of these we fitted a one-hit formula to the zero and maximum dose data points, then examined the relation of the fitted curve to the incidence rate observed at the mid-dose, with and without adjustment for intercurrent mortality. Both underestimates and overestimates of risk at mid-dose occurred substantially more often than expected by chance. We cannot tell whether such underestimates would occur at lower doses, but offer six biological reasons why underestimates might be expected. In a high percentage of animal bioassays, the one-hit formula is not conservative when applied in the usual way to animal data. It remains possible that the one-hit formula may indeed be conservative at sufficiently low doses (below the observational range), but the usual procedure, applied to the usual dose range, can be nonconservative in estimating the slope of the formula at such low doses. Risk assessments for regulation of carcinogens should incorporate some measure of additional uncertainty.     

Regression calibration for logistic regression with multiple surrogates for one exposure

Methods have been developed by several authors to address the problem of bias in regression coefficients due to errors in exposure measurement. These approaches typically assume that there is one surrogate for each exposure. Occupational exposures are quite complex and are often described by characteristics of the workplace and the amount of time that one has worked in a particular area. In this setting, there are several surrogates which are used to define an individual's exposure. To analyze this type of data, regression calibration methodology is extended to adjust the estimates of exposure-response associations for the bias and additional uncertainty due to exposure measurement error from multiple surrogates. The health outcome is assumed to be binary and related to the quantitative measure of exposure by a logistic link function. The model for the conditional mean of the quantitative exposure measurement in relation to job characteristics is assumed to be linear. This approach is applied to a cross-sectional epidemiologic study of lung function in relation to metal working fluid exposure and the corresponding exposure assessment study with quantitative measurements from personal monitors. A simulation study investigates the performance of the proposed estimator for various values of the baseline prevalence of disease, exposure effect and measurement error variance. The efficiency of the proposed estimator relative to the one proposed by Carroll et al. [1995. Measurement Error in Nonlinear Models. Chapman & Hall, New York] is evaluated numerically for the motivating example. User-friendly and fully documented Splus and SAS routines implementing these methods are available (http://www.hsph.harvard.edu/faculty/spiegelman/multsurr.html).     

The Effect of Having Aggressive Friends on Aggressive Behavior in Childhood: Using Propensity Scores to Strengthen Causal Inference

This study used propensity scores to statistically approximate the causal effect of having aggressive friends on aggressive behavior in childhood. Participants were 1355 children (53 percent girls; 31 percent minority) in 97 third and fifth grade classrooms enrolled in the Classroom Peer Ecologies Project. Propensity scores were calculated to control for the impact of 21 relevant confounder variables related to having aggressive friendships and aggressive behavior. The 21 variables included demographic, social, and behavioral characteristics measured at the beginning of the school year. Presence/absence of aggressive friends was measured in the middle of the school year, and aggressive behavior was measured at the end of the school year. Results indicated a significant effect of having one or more aggressive friends on children's aggressive behavior above and beyond the effects of the 21 demographic, social, and behavioral variables. The propensity score model was compared with two other models of peer influence. The strengths and practical challenges of using propensity score analysis to study peer influence were discussed.     

The stories of women who are transferred due to threat of preterm birth

Background

Women at risk of preterm birth before 32 weeks gestation are routinely transferred to facilitate birth at a hospital that has Neonatal Intensive Care. The clinical outcomes of being ‘in-born” improves newborn and neonatal outcomes is well documented. However little is known about the women's experiences when such a complication occurs.