Individual-level space-time analyses of emergency department data using generalized additive modeling

BACKGROUND: Although daily emergency department (ED) data is a source of information that often includes residence, its potential for space-time analyses at the individual level has not been fully explored. We propose that ED data collected for surveillance purposes can also be used to inform spatial and temporal patterns of disease using generalized additive models (GAMs). This paper describes the methods for adapting GAMs so they can be applied to ED data. METHODS: GAMs are an effective approach for modeling spatial and temporal distributions of point-wise data, producing smoothed surfaces of continuous risk while adjusting for confounders. In addition to disease mapping, the method allows for global and pointwise hypothesis testing and selection of statistically optimum degree of smoothing using standard statistical software. We applied a two-dimensional GAM for location to ED data of overlapping calendar time using a locally-weighted regression smoother. To illustrate our methods, we investigated the association between participants’ address and the risk of gastrointestinal illness in Cape Cod, Massachusetts over time. RESULTS: The GAM space-time analyses simultaneously smooth in units of distance and time by using the optimum degree of smoothing to create data frames of overlapping time periods and then spatially analyzing each data frame. When resulting maps are viewed in series, each data frame contributes a movie frame, allowing us to visualize changes in magnitude, geographic size, and location of elevated risk smoothed over space and time. In our example data, we observed an underlying geographic pattern of gastrointestinal illness with risks consistently higher in the eastern part of our study area over time and intermittent variations of increased risk during brief periods. CONCLUSIONS: Spatial-temporal analysis of emergency department data with GAMs can be used to map underlying disease risk at the individual-level and view changes in geographic patterns of disease over time while accounting for multiple confounders. Despite the advantages of GAMs, analyses should be considered exploratory in nature. It is possible that even with a conservative cutoff for statistical significance, results of hypothesis testing may be due to chance. This paper illustrates that GAMs can be adapted to measure geographic trends in public health over time using ED data

Impact Craters and Meteorites: The Egyptian Record

This chapter provides an account of the present Egyptian impact cratering record as well as an overview of the Egyptian meteorite collection. The 45-m-diameter Kamil crater in the East Uweinat District in southwestern Egypt is so far the only confirmed impact crater in Egypt. Due to its exceptional state of preservation Kamil can be considered a typestructure for small-scale impacts on Earth. Enigmatic types of natural glasses including the Libyan Desert glass found in the Great Sand Sea and the Dakhleh glass found near Dakhla Oasis (note that Dakhla, Dakhleh and Dakhla are synonyms) may be products of low-altitude airbursts of large and fragile cometary or asteroidal impactors. A number of circular, cratershaped geological structures superficially resembling impact craters are discussed. To date the Egyptian meteorite collection totals 2 falls, including the ~10 kg Martian meteorite Nakhla that has served as a keystone for the understanding of magmatic differentiation processes on Mars, and 76 finds. With the exception of a minority of incidental findings, most Egyptian meteorite finds (~75%) were recovered over the last ~30 years from three dense meteorite collection areas, namely the El-Shaik Fedl, Great Sand Sea and Marsa Alam fields. The exceptional exposures of the Precambrian basement and Paleozoic to Cenozoic sedimentary covers in Egypt offer a good opportunity for the identification of new impact structures. Likewise, Egypt’s vast rocky desert surfaces are of great potential for the collection of meteorites through systematic searches. These prospects are fundamental ingredients for fostering the ongoing development of meteoritics and planetary science in Egypt as disciplines for future scientific endeavor in Africa