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PubMed1992

Assessment of the spatial occurrence of childhood leukaemia mortality using standardized rate ratios with a simple linear Poisson model.

Reports of a suspected cluster of childhood leukaemia cases in West Central Phoenix have led to a number of epidemiological studies in the geographical area. We report here on a death certificate-based mortality study, which indicated an elevated rate ratio of 1.95 during 1966-1986, using the remainder of the Phoenix standard metropolitan statistical area (SMSA) as a comparison region. In the process of analysing the data from this study, a methodology for dealing with denominator variability in a standardized mortality ratio was developed using a simple linear Poisson model. This new approach is seen as being of general use in the analysis of standardized rate ratios (SRR), as well as being particularly appropriate for cluster investigations.

Adolescent↗
PubMed2005

Effect of absorption on the spatial coherence in scalar fields generated by statistically homogeneous and isotropic sources.

We investigate the behavior of the spectral degree of coherence of fluctuating scalar wave fields generated by statistically homogeneous and isotropic sources within absorbing media. In the limit of negligible losses, the degree of coherence is shown to be of a known universal form (sinc function), whereas in the limit of infinite losses it is shown to asymptotically approach the degree of coherence of the source. The intermediate cases are studied for fields produced by sources with Gaussian and sinc-type coherence functions. These studies show that the concept of negligible losses is meaningful only when defined with respect to specific source distribution statistics, and that even for arbitrarily small nonzero losses, the coherence length of the field can be arbitrarily short.

Journal Article↗
PubMedDate not supplied

[Cartography of epidemiologic data. The principal methods of making continuous data discrete and their importance in cartographic representation].

The cartographic representation of continuous quantitative data is often required in studies of the spatial distribution of health indicators. It imposes a succession of choices which directly affect the result obtained. The conversion of continuous data to discrete data is one of the most important steps in the development of epidemiological maps. This article presents the methods currently used to make data discrete, discusses the advantages and disadvantages of each method and assesses their appropriateness for various situations. As an example, and for comparison purposes, we mapped the same series of statistics (relative rates of avoidable male deaths, "associated with the health care system", for "employment zones" in France from 1988 to 1992), using each of the methods discussed.

Algorithms↗
PubMed1984

Geographic distribution of undocumented immigrants: estimates of undocumented aliens counted in the 1980 census by state.

"This article presents estimates of the number of undocumented aliens counted in the 1980 [U.S.] census for each state and the District of Columbia. The estimates, which indicate that 2.06 million undocumented aliens were counted in the 1980 census, are not based on individual records, but are aggregate estimates derived by a residual technique. The census count of aliens (modified somewhat to account for deficiencies in the data) is compared with estimates of the legally resident alien population based on data collected by the Immigration and Naturalization Service in January 1980." Estimates are provided "for each of the states for selected countries of birth and for age, sex, and period of entry categories.... The origins of the undocumented alien population [are described], as well as some of their demographic characteristics. Some of the implications of the numbers and distribution of undocumented aliens are also discussed." This paper was originally presented at the 1984 Annual Meeting of the Population Association of America (see Population Index, Vol. 50, No. 3, Fall 1984, p. 435).

Age Distribution↗
PubMed1989

Clustered distribution and variability in kinetics of transient K channels in molluscan neuron cell bodies.

The spatial distribution of transient K current, IA, was studied using a combination of patch-clamp and whole-cell voltage-clamp techniques. The average IA current density in somatic patches is 0.64 times the current density in the entire axotomized cell body, a finding which suggests that the axon hillock or initial segment of the axon has a higher concentration of IA channels than much of soma. The highest density of active channels during the peak IA is 1/micron2 at a membrane voltage of -20 mV. There is no evidence for a gradient in the distribution of IA channels in the cell body, but the channels are not evenly distributed. The variability in the number of channels per patch for multiple patches on the same neuron is much higher than expected for a random distribution. Statistical analysis of the data yields a coefficient of dispersion of 8.1, a value indicating a high degree of clustering. The utility of this statistic for evaluating channel distributions is discussed. Several lines of evidence suggest that the upper limit for the area of IA channel clusters is approximately 250 micron2. Single-channel currents attributed to IA were recorded in the cell-attached configuration. The voltage dependence of channel opening and inactivation are the same as measured in whole-cell voltage-clamp experiments. The single-channel conductance is about 9 pS in normal saline. Patches 9-30 micron2 in areas that contain IA channels are often devoid of other K channel types, suggesting that IA channels can occur in isochannel clusters. IA inactivation follows an exponential time course in all of the neurons examined, but the time constant of inactivation ranges from 25 to 560 msec in different cells. The voltage dependence of activation and inactivation and the reversal potential of the current are approximately the same in all cells. When multiple patches on the same neuron are studied, it is found that IA inactivates exponentially with approximately the same time constant in each patch, regardless of patch area. The data suggest that each neuron expresses predominantly, and perhaps exclusively, a single type of IA channel with distinct kinetic properties. The wide range of IA inactivation time constants observed in different cell suggests that a large number of channel types are available for expression. Possible mechanisms for generating diversity in channel types are discussed.

Animals↗