Corinne M. Mar

Cycloplegic Refractions in Infants and Young Children

We studied groups of normal infants and infants with amblyopia and esoropia to determine the incidence of infantile astigmatism. Under cycloplegia, 19% of normal infants had astigmatism; this was at least twice the incidence in adults, but less than one-hale that found by noncycloplegic refractions of infants. During the first three postnatal years the incidence of astigmatism and distributions of spherical equivalents and anisometropia did not distinguish normal patients from most of those with esotropia and amblyopia.

Impact of School District Sugar-Sweetened Beverage Policies on Student Beverage Exposure and Consumption in Middle Schools

PURPOSE To determine the associations between 1) exposure to sugar-sweetened beverages (SSB) in middle schools and student consumption of SSB during the school day; and 2) school district policies about SSB and exposure to SSB in schools. METHODS The strength of school district SSB policies was scored on three SSB policy indicators. Student SSB consumption at school was assessed by a self-administered Beverage and Snack Questionnaire. Exposure to SSB at school was defined as the number of vending slots and SSB venues as determined on-site at each school. Multivariate analysis considered the multilevel nature of the data. RESULTS Data from 9151 students in 64 middle schools in 28 districts were used in the analysis. With schools as the unit of analysis, the proportion of students who consumed any SSB at school ranged from 19.2% to 79.8%. SSB exposure was a significant predictor of SSB consumption (beta=.157, p < .001). SSB consumption was not significantly associated with the size of the school, the racial or ethnic composition of the schools students, or the proportion of students eligible for free and reduced price meals. District SSB policy scores ranged from 0 to 6 with a mean score of 3.25 (+/-2.15). District SSB policy was a significant predictor of SSB exposure (beta=-9.50, p < .0002). CONCLUSIONS School district SSB policies and exposure to SSB in middle schools are associated with student SSB consumption. Interventions to improve policies and their implementation may offer opportunities to improve the diets of adolescents.

The structure of schizophrenic symptoms: a meta-analytic confirmatory factor analysis

To quantitatively review all presently available evidence about the interrelations between positive and negative schizophrenic symptoms, we created an aggregate matrix of the intercorrelations among schizophrenic symptoms by combining data from 28 independent samples using meta-analytic procedures (net bivariate dfs ranging from 683 to 1657). Using confirmatory factor analyses, we then statistically compared four theoretically derived models of the structure of schizophrenic symptoms. Although a three-factor model (Liddle, 1987) best fit the data, results suggest that either more factors or different symptoms are required to account well for the latent structure underlying schizophrenic symptomatology. The nature of such augmented approaches, the opportunities and constraints inherent to multifactorial models, and the limitations of current instruments are discussed.

Infant eye movement asymmetries : stationary counterphase gratings elicit temporal-to-nasal optokinetic nystagmus in two-month-old infants under monocular test conditions

Tested monocularly, young infants classically show directional eye movement asymmetries, with optokinetic nystagmus (OKN) being more readily elicited by stimuli moving in the temporal-to-nasal (T-N) than in the nasal-to-temporal (N-T) direction. Since a counterphase grating is physically identical to two superimposed sinusoidal components moving in opposite directions, we wondered whether or not a counterphase grating would elicit T-N OKN in monocularly tested infants. Two-month-old infants were tested in a motion nulling paradigm. Under monocular test conditions, all infants showed T-N OKN in response to the counterphase grating. The results suggest that the young infants visual system represents the counterphase grating in terms of its T-N and N-T components, and reduces the effective contrast of the N-T component prior to the generation of OKN. The results are discussed in relation to models of OKN asymmetries and the responses of direction-selective neurons to counterphase gratings.

Estimating the size of populations at high risk for HIV using respondent-driven sampling data

The study of hard-to-reach populations presents significant challenges. Typically, a sampling frame is not available, and population members are difficult to identify or recruit from broader sampling frames. This is especially true of populations at high risk for HIV/AIDS. Respondent-driven sampling (RDS) is often used in such settings with the primary goal of estimating the prevalence of infection. In such populations, the number of people at risk for infection and the number of people infected are of fundamental importance. This article presents a case-study of the estimation of the size of the hard-to-reach population based on data collected through RDS. We study two populations of female sex workers and men-who-have-sex-with-men in El Salvador. The approach is Bayesian and we consider different forms of prior information, including using the UNAIDS population size guidelines for this region. We show that the method is able to quantify the amount of information on population size available in RDS samples. As separate validation, we compare our results to those estimated by extrapolating from a capture-recapture study of El Salvadorian cities. The results of our case-study are largely comparable to those of the capture-recapture study when they differ from the UNAIDS guidelines. Our method is widely applicable to data from RDS studies and we provide a software package to facilitate this.

Evaluating Variance Estimators for Respondent-Driven Sampling

Author(s): Spiller, Michael W; Gile, Krista J; Handcock, Mark S; Mar, Corinne M; Wejnert, Cyprian