Modeling the Ames Salmonella/microsome assay.

Of the many short-term tests for mutagenicity that have been proposed in recent years, the Ames Salmonella/microsome assay is the single most widely used and most thoroughly validated in vitro test system. This assay uses cells cultured in a soft agar containing a trace amount of histidine to allow growth of auxotrophic bacteria, and is designed to detect reverse mutations from auxotrophic cells to histidine-independent prototrophic cells. In this paper, statistical models that have been proposed for the analysis of Ames test data are reviewed, including those of a mechanistic and empirical nature. An extension to the class of biologically based models derived by Margolin, Kaplan, and Zeiger (1981, Proceedings of the National Academy of Sciences 78, 3779-3783) is proposed by allowing for diffusion of histidine within the plate agar. Quasi-likelihood methods for estimating the model parameters are presented, and applied to 1,120 data sets from a recent collaborative trial sponsored by the International Programme on Chemical Safety.

Planning for rabies control in Ontario.

Ten geographic cells of rabies cases were identified within southern Ontario. Some had regular 3-year peaks, whereas others had weak cycles with mean periods of up to 9 years. Incidence of rabies was related to soil types (highest on sandy and clay loams), land use (abundant where hay and pasture were dominant), and drainage (poor drainage supported only low levels of rabies). A spatial stochastic simulation model is being used to evaluate risks and tactics associated with reduction of rabies by use of vaccine baits. The model indicated that persistence of rabies is unlikely in areas with less than 4,000 km2 of contiguous fox habitat. In sensitivity tests the model was most affected by the values of four input parameters: rate of contact among foxes, incubation period of rabies, fox density, and a density-dependent feedback that reduces fox recruitment when density approaches or exceeds a predetermined "carrying capacity." In a majority of model experiments, a single vaccination of 60% of a fox population eradicated rabies, but only if vaccination took place just after a rabies outbreak, when the number of both foxes and rabid animals was reduced. Rabies control will probably be applied to individual cells or clusters of cells rather than to the entire 98,000 km2 enzootic zone, at least at first. If rabies is eradicated the fox populations may increase, but modestly. Skunks were more important than foxes as vectors of rabies in urban Ontario. Since there is no effective oral rabies vaccine for skunks, skunks were trapped alive and vaccinated by injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Statistical method for evaluating human thoracolumbar spinal curves in the sagittal plane: a preliminary report.

This study was conducted to develop a statistical method of analyzing human thoracolumbar curves in the sagittal plane. Spinal tracings were obtained from 30 women by recording directly from the body surface, using a draftsman's flexible rule, transferring curves to graph paper, and making cubic spline and principal component analyses. Results were: an accurate method of analyzing spinal curves; accurate analysis of curves at an average overall residual standard deviation of 0.7 mm; component analysis suggesting that this method can be used to establish normal values for specific populations of known age, race, and sex, and to categorize individual curves.

The contribution of fetal-newborn complications to motor and cognitive deficits.

A total of 364 selected high-risk premature and mature infants were studied prospectively to assess the relationship between fetal-newborn complications and motor and cognitive deficits identified during the first year of life. Deficits occurred in 24 per cent of the children: 14 per cent had one or more major deficit and the other 10 per cent had one or more minor deficit. Prematurity was one of the fetal-newborn complications not associated with deficits at one year. Complications that were associated with deficits included fetal hypoxia, respiratory difficulties, infection and newborn encephalopathy. There was also a significant association between fetal hypoxia, newborn respiratory complications, infection and newborn encephalopathy, which is in keeping with the concept that the first three may be mechanisms in CNS injury and subsequent deficits, while newborn encephalopathy reflects the injury and is an important predictor of such deficits.

Resurfacing elbow prosthesis: shape and sizing of the humeral component.

The sizing and dimensioning of a new unconstrained elbow prosthesis makes use of a geometric axis for humeral articulating surface definition, an axis which is precisely positioned with respect to extra-articular anatomical landmarks. The geometry of the joint was determined by a slicing and digitization technique. It was found that for the humerus an axisymmetric surface is evident and that there exists a centroidal axis which is mostly linear except for a portion at the posterior lateral flange of the trochlea. Sizing studies were carried out on dry bone anatomical specimens and, using a standardized X-ray technique, on the elbows of volunteer subjects. Seven dimensions were chosen for statistical analysis of the joint. A multi-variate normal distribution model, using only the first principal component was found to account for 70% of the variance; components 2 and 3 explained a further 19%. From this analysis, one series of three and five sizes of prosthetic dimensions were established for 95% overall coverage of population.