Willingness to participate in a national seroprevalence study of HIV infection.

This paper examines the impact of the social dimension of AIDS on a person's willingness to participate in a hypothetical national seroprevalence study of HIV infection. Data from the AIDS supplement of the 1987 National Health Interview Survey provided information about the sociodemographic characteristics and AIDS-related variables and the expressed willingness to participate in a national serosurvey. A multivariate logistic regression model was used to evaluate simultaneously associations between the sociodemographic variables and AIDS-related variables with willingness to participate. Results show that those with sociodemographic characteristics most dissimilar from reported AIDS cases were least willing to participate while those with a high knowledge about AIDS, experience of the HIV test or tested people, and higher perceptions of risk were more willing to participate. We found two exceptions to this general result. First, respondents with no knowledge about AIDS, but a higher level of education, were less willing to participate than those with no knowledge and a lower level of education. Second, respondents with a higher perception of risk and a higher level of education were also less willing than those with high perception of risk and less education.

Cost savings associated with increased safety belt use in Iowa, 1987-1988.

Although safety belt use increases after passage of a safety belt law, the statewide direct and indirect cost savings associated with increased safety belt use after a belt use law has been enacted is not known. We analyzed a subset of data from the Iowa Safety Restraint Assessment consisting of 997 injured motor vehicle occupants treated at any of 11 Iowa hospitals from throughout the state between November 1987 and March 1988. We found that injuries were more serious and that more deaths and cases of permanent disability occurred among persons who did not wear safety belts. Failure to use safety belts was independently associated with higher payments to hospitals by health care insurers and individuals in nearly all age, sex, and vehicle speed categories. Lifetime direct and indirect cost savings associated with Iowa's safety belt law for persons injured in one year were estimated to be $69.5 million.

Selected hormonal changes with summer fescue toxicosis.

The effects of fescue endophyte content (low, 16 or high, 44% of tillers examined) and of N fertilization rate (low, 134 kg N.ha-1.yr-1 or high, 336 kg N.ha-1.yr-1) upon serum prolactin (PRL) in Angus steers were examined. Jugular blood samples for serum PRL determination were taken before (basal) and after thyrotropin releasing hormone (TRH) administration (stimulated). Areas under both the basal and stimulated PRL curves were calculated. While areas under the PRL curves varied with length of photoperiod, high endophyte content resulted in a consistent PRL suppression during 1984. During four time periods in 1984 (May to October), areas under the PRL curves [basal and(or) TRH stimulated] were suppressed (P less than .05) with high endophyte on three dates. Although basal areas under the PRL curves in 1983 were nonsignificantly suppressed with high endophyte, there was a suppression (P less than .05) post-TRH in October with high endophyte. There was no effect of N on PRL areas in either year. No relationship was found to exist between basal PRL areas and average daily gains as computed to encompass a period 2 wk before and after a blood collection date. Mean basal growth hormone (GH) concentration as determined from one bleeding date were elevated (P less than .05) in steers on high compared with low endophyte (7.9 and 6.2 ng/ml +/- 1.1 overall SE, respectively). There was no effect of treatment on TRH-stimulated serum GH values. Mean basal serum insulin values ranged from 13.2 to 17.5 microU/ml (+/- 1.2 overall SE) and were not affected by treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

A constrained empirical Bayes estimator for incidence rates in areas with small populations.

Maps that show the geographic distribution of incidence rates can be useful tools for analysing spatial variation in mortality and morbidity. To attain the necessary geographic resolution, however, production of such maps often requires estimation of incidence in areas with small populations where the observed rates may be highly unstable. Manton et al. have presented an empirical Bayes stabilization procedure in which the observed rate is combined with an area-specific estimate of the underlying incidence. The approach allows for the mapping of outcomes with varied and possibly unknown etiologies without necessitating covariate dependent modelling of the expected rate. The empirical distribution of a collection of these estimates, however, may not provide an adequate description of the dispersion among the true rates. As a result, decisions based on the histogram of the empirical Bayes estimates may be suspect. We propose a modified version of the approach in which the mean and sample variance of the ensemble of estimates are constrained to equal the appropriate moments of the posterior distribution. The resulting collection of constrained empirical Bayes estimators has nearly the stability of the unconstrained approach and provides an improved estimator of the true rate distribution. We illustrate use of the estimator by producing stabilized county-level maps of U.S. fire- and burn-related mortality rates and validate the analytic results using a simulation analysis.

Estimating sample size for epidemiologic studies: the impact of ignoring exposure measurement uncertainty.

Sample size requirements for epidemiologic studies are usually determined on the basis of the desired level of statistical power. Suppose, however, that one is planning a study in which the participants' true exposure levels are unobservable. Instead, the analysis will be based on an imprecise surrogate measure that differs from true exposure by some non-negligible amount of measurement error. Sample size estimates for tests of association between the surrogate exposure measure and the outcome of interest may be misleading if they are based solely on the anticipated characteristics of the distribution of surrogate measures in the study population. We examine the accuracy of sample size estimates for cohort studies in which a continuous surrogate exposure measure is subject to either classical or Berkson measurement error. In particular, we evaluate the consequences of not adjusting the sample size estimation procedure for tests based on imprecise exposure measurements to account for anticipated differences between the distributions of the true exposure and the surrogate measure in the study population. As expected, failure to adjust for classical measurement error can lead to underestimation of the required sample size. Disregard of Berkson measurement error, however, can result in sample size estimates that exceed the actual number of participants required for tests of association between the outcome and the surrogate exposure measure. We illustrate this Berkson error effect by estimating sample size for a hypothetical cohort study that examines an association between childhood exposure to radioiodine and the development of thyroid neoplasms.

Empirical Bayes methods for stabilizing incidence rates before mapping.

The epidemiologic utility of mapping and ranking incidence rates is often questioned owing to instability of the observed incidence values in areas with small populations. Spurious fluctuations in the observed rates caused by this instability can mask true spatial and temporal trends in risk. To produce maps with the required level of geographic resolution, yet based on reliable estimates, it is desirable to reduce the random variation in the observed rates before mapping. In this paper, we describe the empirical Bayes approach for obtaining stabilized incidence estimates. We begin by deriving Bayes rate estimators and then illustrate how using the observed rates to estimate unknown distributional information leads to the empirical Bayes formulation. A drawback of the approach is that the histogram of the empirical Bayes rate estimates may be narrower than the true distribution of risk. We outline a constrained empirical Bayes approach that produces improved estimators for the true distribution of the unknown rates. We include discussions of relevant previous applications of empirical Bayes methods to rate mapping problems and an evaluation of the strengths and weaknesses of the approach.

Relation of soil and plant magnesium to nutrition of animals and man.

The importance of Mg for the production and quality of crops grown on soils, as well as the health and productivity of animals and humans that consume these crops, is the focus of this paper. The Mg requirements and resulting concentrations of most crops are sufficiently high that primary Mg deficiency in animals consuming these crops is rare, providing the crops receive adequate Mg from soil solution for normal growth. Hypomagnesemic grass tetany or conditioned Mg deficiency occurs in mature ruminant lactating females grazing cool season forages. Grass tetany occurrence is seasonal, and is often related to heavy lactation demand for Mg. Another factor is reduced bioavailability of Mg to the ruminant associated with high concentrations of crude protein and K, as well as associated changes in plant constituents such as lowered soluble carbohydrate content and increased levels of higher fatty acids and organic acids. The high water content in the immature grass tissue being grazed may also result in less efficient Mg absorption by animals. Grass tetany studies at Watkinsville, Ga., revealed that high N fertilization of tall fescue pastures from poultry manure, or inorganic fertilizer increased incidence of hypomagnesemic grass tetany, and hypomagnesemia. Regression analyses indicate highly significant correlations between Mg levels in blood serum and forage Mg, K and crude protein. The results between years and experimental pastures clearly suggested that individual years and experimental pasture relationships were different. The following was concluded with regard to the relationship of soil and plant Mg to human nutrition: first, surveys of agricultural raw products indicate that genetic factors (species and cultivars) appear to have more effect on plant Mg composition than do soil and environmental factors. Second, patterns of Mg intake by humans in the USA suggest that about 50% of their intake is from foods of plant origin. About half of this intake is from vegetables, where increases in Mg concentration may be achieved by changing cultural practices. While direct supplementation with Mg appears more efficacious in prevention of Mg deficiency in humans, research with susceptible ruminants indicates that complete protection can only be assured by adequate daily intake of bioavailable Mg in their consumed food. Similar situations would be expected to prevail in humans.

Impact of the human immunodeficiency virus epidemic on mortality trends in young men, United States.

Following a long-term decline, death rates in men 25-44 years of age increased from 212 deaths/100,000 in 1983 to 236 deaths/100,000 in 1987. To assess the impact of human immunodeficiency virus (HIV) infections on this trend and to identify causes that are increasing in association with the HIV epidemic, we analyzed national mortality statistics and compared death rates in states with high and low incidence of acquired immunodeficiency syndrome (AIDS). In 1987, there were 10,248 deaths with HIV infection, AIDS, or conditions in the AIDS surveillance definition assigned as the underlying cause, representing 11 percent of deaths for men in this age group compared to less than 1 percent in 1980. In addition, deaths with other underlying causes, such as other infections, drug abuse, and unknown/unspecified causes, had diverging and higher rates in states with high versus low AIDS incidence. In the absence of deaths due to HIV/AIDS and excess deaths due to these associated conditions, we estimate that death rates for men 25-44 years of age would have been 201-209/100,000 in 1987. For 1987, approximately 70-90 percent of HIV-related deaths were reported through national AIDS surveillance. The HIV epidemic has led to a reversal in mortality trends and to increases in various causes of death for young men.

Air quality and pediatric emergency room visits for asthma in Atlanta, Georgia, USA.

Pediatric emergency room visits for asthma were studied in relation to air quality indices in a spatio-temporal investigation of approximately 130,000 visits (approximately 6,000 for asthma) to the major emergency care centers in Atlanta, Georgia, during the summers of 1993-1995. Generalized estimating equations, logistic regression, and Bayesian models were fitted to the data. In logistic regression models comparing estimated exposures of asthma cases with those of the nonasthma patients, controlling for temporal and demographic covariates and using residential zip code to link patients to spatially resolved ozone levels, the estimated relative risk per 20 parts per billion (ppb) increase in the maximum 8-hour ozone level was 1.04 (p < 0.05). The estimated relative risk for particulate matter less than or equal to 10 microm in aerodynamic diameter (PM10) was 1.04 per 15 microg/m3 (p < 0.05). Exposure-response trends (p < 0.01) were observed for ozone (>100 ppb vs. <50 ppb: odds ratio = 1.23, p = 0.003) and PM10 (>60 microg/m3 vs. <20 microg/m3: odds ratio = 1.26, p = 0.004). In models with ozone and PM10, both terms became nonsignificant because of collinearity of the variables (r= 0.75). The other analytical approaches yielded consistent findings. This study supports accumulating evidence regarding the relation of air pollution to childhood asthma exacerbation.