Cervical cancer in young Americans.
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Adult↗
Biomedical subjects
S Selvin
Publications and source records attributed to S Selvin.
A study of multiple causes of death in California: 1955 and 1980.
Multiple cause of death patterns in California for 1980 were compared to a similar study of deaths conducted in 1955. Primary underlying causes of death changed, mainly reflecting the emergence of respiratory cancer as a major cause of death in 1980. The number of causes reported per death increased from 1955 to 1980, in all age and sex groups. Diseases of the arteries and pneumonia, which are among the most common underlying causes of death, appeared more often on death certificates in both 1955 and 1980 as contributing causes than as underlying the death. Diabetes was studied in detail in the 1955 report, and comparisons were made in 1980 to show increases in the proportions of deaths with this disease and corresponding increases in its prevalence among the living population from the National Health Survey. Multiple cause of death data can provide further information on the prevalence of a fatal disease in a population and its relative role in contributing to mortality, and can also provide new information on diseases that contribute to deaths, which was not previously available in population-based studies of single cause of death.
Adult↗
The effect of autocorrelation on the estimation of workers' daily exposures.
Daily 8-hr time-weighted average (TWA) measurements may not be independent since production rates, maintenance schedules, work practices, and ventilation can result in trends where consecutive values are correlated (autocorrelation). A sampling program which involves collection of measurements on consecutive days, therefore, can result in biased estimates of the mean and variance of the exposure distribution if a high degree of autocorrelation exists. Three simulated data sets were examined to assess the effects of autocorrelation on the estimation of exposure distributions. Results indicated that about 30% of estimated mean values from a highly-autocorrelated series were outside the 95% confidence interval observed for an uncorrelated series. Three data sets obtained from actual workplaces were found to have relatively little autocorrelation. This suggests that for workplaces such as those analyzed here, a random sampling program may not be necessary, and sequential sampling may produce accurate estimates of the parameters of the exposure distribution.
Air Pollutants, Occupational↗
OSHA's permissible exposure limits: regulatory compliance versus health risk.
Workplace exposures to airborne chemicals are regulated in the U.S. by the Occupational Safety and Health Administration (OSHA) via the promulgation of permissible exposure limits (PELs). These limits, usually defined as eight-hour time-weighted average values, are enforced as concentrations never to be exceeded. In the case of chronic or delayed toxicants, the PEL is determined from epidemiological evidence and/or quantitative risk assessments based on long-term mean exposures or, equivalently, cumulative lifetime exposures. A statistical model was used to investigate the relation between the compliance strategy, the PEL as a limit never to be exceeded, and the health risk as measured by the probability that an individual's long-term mean exposure concentration is above the PEL. The model incorporates within-worker and between-worker variability in exposure, and assumes the relevant distributions to be log-normal. When data are inadequate to estimate the parameters of the full model, as it is in compliance inspections, it is argued that the probability of a random measurement being above the PEL must be regarded as a lower bound on the probability that a randomly selected worker's long-term mean exposure concentration will exceed the PEL. It is concluded that OSHA's compliance strategy is a reasonable, as well as a practical, means of limiting health risk for chronic or delayed toxicants.
Air Pollutants, Occupational↗
The probability of finding suitable directed donors.
A series of tables based on mathematical calculations is given as guidelines for the number of directed donors needed by members of various ethnic/racial groups to provide a desired number of units of blood with a selected probability of achieving this result. From these tables, certain conclusions can be drawn. Unrelated donors who do not know their blood type are an inefficient source of directed donors. Rh-negative patients are unlikely to obtain enough directed-donor units from either related or unrelated donors with confidence unless these donors known their blood type. In general, siblings, parents, and offspring are the most efficient directed donors from the standpoint of compatibility. Cousins, uncles, aunts, nieces, and nephews are not much more likely to be compatible than unrelated donors are. It is easier to obtain suitable directed-donor units among Hispanics than among whites, blacks, or Asians, due to their skewed blood group frequencies. In general, using O-negative directed donors for Rh-positive recipients does not significantly increase the likelihood of finding suitable donors.
Blood Donors↗
Density equalized map projections: a method for analysing clustering around a fixed point.
Cases plotted on a geopolitical map entail difficulties in interpretation and analysis because of variable population density in the study area. Density equalized map projections (DEMPs) eliminate the distribution of the resident population as an interfering influence by transforming map area to be proportional to population. This paper discusses a transformation algorithm, its properties, and develops statistical methods to detect clustering of cases around a fixed point for data plotted on DEMPs. We suggest two numeric methods where exact solutions are too complicated or do not exist. Finally, we illustrate these methods using data from Denver and Jefferson counties in Colorado to investigate whether lung cancer and leukaemia incidence patterns are associated with plutonium exposure from the Rocky Flats plant site.
Adult↗
"Rates" of birth defects.
The proportion of children born with a particular defect is not a "birth defect rate" but, rather, a prevalence proportion. The implications of confusing a rate and a proportion are discussed in terms of the interpretation of birth defect data. It is recommended that "prevalence proportion" or "prevalence" be used to report the frequency of various defects rather than the often-used "prevalence rate."
Biometry↗
Transformations of maps to investigate clusters of disease.
An approach is presented to display and analyze epidemiologic data using population density equalized maps (cartograms). The algorithm for generating these maps is discussed. A specific method for statistically analyzing plotted data is given, followed by an application of maps and analysis to 73 sets of age-, race-, sex-, and site-specific cancer incidence data. The data were obtained from the Surveillance, Epidemiology and End Results project for San Francisco City/County (1978-1981) and combined with 1980 U.S. Census data.
Adult↗
An examination of three spatial disease clustering methodologies.
Patterns of disease in space are often analysed to determine whether a relationship exists between a disease outcome and environmental exposures. This report examines the performance of three cluster analytical methods when applied to a single data set. These methods, designed to assess the purely spatial variation of events, have been examined to assess their ability to detect clustering in an area where disease rates have previously been shown to be significantly elevated. The ability of these methods to detect spatial clustering was also examined using simulation techniques. All three methods were found to be poor at detecting spatially localized disease rates which were approximately three time the expected rate, as measured by the relative risk.
California↗
The onset of decline in ischemic heart disease mortality in the United States.
Temporal and spatial patterns of the onset of the decline in ischemic heart disease mortality in the United States for each of the 48 contiguous US states and the District of Columbia are examined for the years 1955-1978 for age-sex-race-specific mortality. Mortality rates are derived from National Center for Health Statistics mortality data, and a polynomial interpolation is used to estimate intercensal population counts employing 1950, 1960, 1970, and 1980 US Census data. A quadratic regression equation is used to estimate the date of highest rate, which marks the beginning of the decline for each of the US states. The temporal distribution of the onset of the decline among men occurred primarily between 1960 and 1965. Among women, the onset of decline was more variable. Furthermore, strong and regular spatial patterns were seen among the groups examined and these impressions are supported by statistical analysis. California, Maryland, and the District of Columbia were early decliners in most groups studied, whereas states in the southeast were consistently among the last to experience the onset of decline. These patterns suggest the existence of an underlying phenomenon accounting for the spread or diffusion of the onset of decline in ischemic heart disease mortality.
Adult↗
Micronuclei in cytokinesis-blocked lymphocytes as an index of occupational exposure to alkylating cytostatic drugs.
Micronucleated peripheral blood lymphocytes were analysed in cytochalasin-B-treated binucleated lymphocytes using cytocentrifuged preparations. Increased numbers of micronuclei were observed in lymphocytes of groups of workers from industry and hospitals potentially exposed to cyclophosphamide. The finding was independent of the age of the subjects, which was also correlated with micronuclei formation.
Adult↗
Two issues concerning the analysis of grouped data.
Simple statistical models are used to illustrate two important issues arising in the analysis of grouped data. The consequences are explored of grouping continuous data and analyzing the resulting contingency table. Specifically, an expression for the loss of power is derived when and odds ratio is used to assess risk measured by a continuous variable. Also explored are the consequences of employing correlation and regression coefficients to analyze summary variables derived from grouped data (ecologic data). An expression is given that demonstrates the magnitude of a bias (ecologic fallacy) resulting from analyzing a specific type of grouped data.
Data Collection↗
A note on the assessment of exposure using one-sided tolerance limits.
Conceptual problems with OSHA's use of an absolute standard have led to alternative methods of assessing exposures to toxic materials in the workplace. One of these methods employs a one-sided tolerance limit. This statistical approach is explored from three points of view--identifiability, sampling strategies and statistical power. In general, assessing risk in the work environment with tolerance limits is found to give inadequate answers in several important respects.
Humans↗
A method for evaluating the mean exposure from a lognormal distribution.
OSHA's risk assessments, made in support of new standards, implicitly assume that workers are exposed at the level of the PEL on the average over their working lifetimes. This approach seems to be justified at least in cases where the toxicant is eliminated slowly from the critical site in the body. Thus, there are situations where the industrial hygienist should seek to evaluate worker mean exposure overtime. A simple testing procedure is proposed for determining whether the mean exposure of a lognormally-distributed exposure series, mu c, is less than the Permissible Exposure Limit (PEL) at desired levels of significance and power. With the assumption that the exposures are described adequately by a longnormal distribution, the method allows realistic exposure scenarios where mu c less than PEL to be declared acceptable with between two and fifty 8-hr TWA measurements, depending upon the value of muc and the level of variability. Application of the methods to three industrial data sets indicates that the approach is viable.
Air Pollutants, Occupational↗
Spatial distribution of disease: three case studies.
Maps transformed so as to have constant density of residential population were used to analyze the spatial distribution of disease in three specific areas. Each area had received recent attention because of suspected environmental pollution. The area adjacent to the Rocky Flats Facility (CO) was examined to identify any association between possible plutonium releases and increases in lung cancer or leukemia incidence. The industrial area of northern Contra Costa County (CA) was studied to explore a relationship between petrochemical industrial emissions and histologic-specific lung cancers. Finally, a suspected increase in the risk of congenital cardiac defects possibly related to pollution of the Santa Clara County (CA) water supply was investigated. No evidence of elevated risk of disease was found to be associated with either the Rocky Flats Facility or the polluted water of Santa Clara County. An increase in lung cancer, found by other investigators in earlier years, was shown to persist in association with industrial emissions in Contra Costa County.
Adult↗
The influence of averaging time on the distribution of exposures.
Personal exposures to toxic airborne agents in the work environment often are approximately log-normally distributed. While the arithmetic mean of these distributions is independent of the averaging time of the measurement in a stationary environment, this is not the case for the variance. In general, the variance decreases with increasing averaging time, but the rate of decrease depends upon the autocorrelation structure of the exposure time series. If the autocorrelation structure can be determined, a knowledge of the parameters of the distribution of exposures at one averaging time allows the estimation of those for any other averaging time. Regardless of the autocorrelation situation, these results suggest that current ACGIH guidelines for assessing short-term exposures need examination and may require modification.
Air Pollutants, Occupational↗
Ecologic regression analysis and the study of the influence of air quality on mortality.
This presentation focuses entirely on the use and evaluation of regression analysis applied to ecologic data as a method to study the effects of ambient air pollution on mortality rates. Using extensive national data on mortality, air quality and socio-economic status regression analyses are used to study the influence of air quality on mortality. The analytic methods and data are selected in such a way that direct comparisons can be made with other ecologic regression studies of mortality and air quality. Analyses are performed by use of two types of geographic areas, age-specific mortality of both males and females and three pollutants (total suspended particulates, sulfur dioxide and nitrogen dioxide). The overall results indicate no persuasive evidence exists of a link between air quality and general mortality levels. Additionally, a lack of consistency between the present results and previous published work is noted. Overall, it is concluded that linear regression analysis applied to nationally collected ecologic data cannot be used to usefully infer a causal relationship between air quality and mortality which is in direct contradiction to other major published studies.
Air Pollutants↗
The probability of exclusion or likelihood of guilt of an accused: paternity.
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Bayes Theorem↗