Classification errors of dependent variables can distort the results of observational studies. To reduce misclassification from our multicentre observational study of abortion complications, we extended the methodology of Lawrence and Greenwald for use in situations of unequal sample sizes and implemented both an office review and a field review. We reabstracted 424 reported complications and a random sample of 364 reported non-serious cases from 12 institutions participating in our study. In total, 30 per cent of the reported serious complications turned out to be misclassified: the office review detected 74 per cent of the total number of misclassifications with the remainder found in the field review. Because, with our particular data base, we estimated expending only 15 per cent of the total resources with our office effort, this represented the most cost-efficient approach to reducing classification errors. By eliminating the false positives from our study, we forced the specificity to 1.00 which produced both an unbiased estimate of the relative risk and an increase of 4 per cent to 63 per cent in the power of our study.

Abortion, Spontaneous↗

PubMedDate not supplied

Phototransduction: modeling the primate cone flash response.

We have developed a new model of phototransduction that accounts for the dynamics of primate and human cone flash responses in both their linear and saturating range. The model incorporates many of the known elements of the phototransduction cascade in vertebrate photoreceptors. The input stage is a new analytic expression for the activation and inactivation of cGMP-phosphodiesterase (PDE). Although the Lamb and Pugh (1992) model (of a delayed ramp for the rising phase of the PDE response in amphibian rods) provided a good fit for the first 2 log units of stimulus intensity without parameter adjustments, the remaining 4 log units of the data required nonlinear modifications of both delay and gain (slope). We show that this nonlinear behavior is a consequence of the delay approximation and develop a completely linear model to account for the rising phase of amphibian rod photocurrent responses over the full intensity range (approximately 6 log units). We use the same dynamic model to account for primate cone responses by decreasing the time constants of PDE activation and introducing an enhanced inactivation process. This PDE response activates a nonlinear calcium feedback stage that modulates guanylate cyclase synthesis of cyclic GMP. By adjustment of the throughput and feedback parameters, the full model successfully captures most of the features of the primate and human cone flash responses throughout their dynamic range. Our analysis suggests that initial processes in the transduction cascade may be qualitatively different from comparable processes in rods.

3',5'-Cyclic-GMP Phosphodiesterases↗

PubMedDate not supplied

Human symmetry detection exhibits reverse eccentricity scaling.

Human symmetry detection in dense patterns exhibits a spatial integration range that becomes narrower with distance of the symmetry axis from the fovea. This narrowing violates the general properties of eccentricity that have been found for all previous visual cortical areas, tasks, and assessment techniques. This reverse eccentricity scaling may, in conjunction with the long-range matching properties for symmetry described in Tyler and Hardage (1996), imply that symmetry is processed by a specialized cortical area with non-retinotopic neural architecture.

Fovea Centralis↗

PubMedDate not supplied

Visual acuity development in normal and abnormal preterm human infants.

The grating acuity of preterm infants was determined by measurements of the visual evoked potential (VEP) produced by phase alternation of sinusoidal luminance gratings. The development of visual acuity in healthy preterm infants appears to be accelerated when compared with full term infants of the same post-conceptual age. Cortical insults and the more advanced stages of retinopathy of prematurity may adversely affect acuity development as indexed by the VEP. Preterm twins also appear to have lower acuity than preterm monoparous infants.

Evoked Potentials, Visual↗

PubMedDate not supplied

IUD insertion practices in the United States and Puerto Rico, 1973.

Explore the source record for details and available documents.

Adolescent↗

PubMedDate not supplied

State epidemiology programs and state epidemiologists: results of a national survey.

In 1983, the State Epidemiologists in 46 States completed a survey questionnaire describing the professional qualifications, training, and experience of State health department epidemiologists and the scope of participation by the State Epidemiologists and their staffs in public health programs. The survey identified 224 State health department epidemiologists (estimated U.S. ratio 1.1 per million population). A State health department epidemiologist was most often male (80 percent), frequently (57 percent) was a physician, had an average age of 41 years, and had worked as an epidemiologist for 9 years. Participation in public health programs (either by supervising or providing consultation) by the State Epidemiologists and their staffs focused mainly on general epidemiology and communicable disease programs; fewer than half had participated in programs relating to the health of women and children, chronic diseases, injuries, or in other programs directed towards preventing premature mortality. Recently, the State Epidemiologists have been trying to broaden their activities into these areas; however, the demands created by the acquired immunodeficiency syndrome (AIDS) will mostly likely slow this process. Based on the overall findings and collective experience, it was concluded that State health departments have too few epidemiologists to address the wide variety of important public health problems facing our communities. It was proposed that each State health department have at least four epidemiologists (including one or more physician epidemiologists) and at least one master's level biostatistician and that the epidemiologists-per-population ratio not be less than 1 per million.

Adult↗