An improved model for prediction of resuspension

A complete, historical dataset is presented of radionuclide resuspension-factors. These data span six orders of magnitude in time (ranging from 0.1 to 73,000 d), encompass more than 300 individual values, and combine observations from events on three continents. These data were then used to derive improved, empirical models that can be used to predict resuspension of trace materials after their deposit on the ground. Data-fitting techniques were used to derive models of various types and an estimate of uncertainty in model prediction. Two models were found to be suitable: a power law and the modified Anspaugh et al. model, which is a double exponential. Though statistically the power-law model provides the best metrics of fit, the modified Anspaugh model is deemed the more appropriate due to its better fit to data at early times and its ease of implementation in terms of closed analytical integrals.     

An improved model for professional conferences and workshops

A cooperative learning method designed to increase learning and other benefits to participants is presented. Small group problem-solving from case studies or story narratives provides a way to overcome the limitations of conventional lecture presentations. An example that used a case study in small groups during a breakout session at a scientific conference to improve skills in intervention design and research evaluation is described. © 1996 Wiley-Liss, Inc.     

Iowa radon leukaemia study: a hierarchical population risk model for spatially correlated exposure measured with error

This paper presents a Bayesian model that allows for the joint prediction of county-average radon levels and estimation of the associated leukaemia risk. The methods are motivated by radon data from an epidemiologic study of residential radon in Iowa that include 2726 outdoor and indoor measurements. Prediction of county-average radon is based on a geostatistical model for the radon data which assumes an underlying continuous spatial process. In the radon model, we account for uncertainties due to incomplete spatial coverage, spatial variability, characteristic differences between homes, and detector measurement error. The predicted radon averages are, in turn, included as a covariate in Poisson models for incident cases of acute lymphocytic (ALL), acute myelogenous (AML), chronic lymphocytic (CLL), and chronic myelogenous (CML) leukaemias reported to the Iowa cancer registry from 1973 to 2002. Since radon and leukaemia risk are modelled simultaneously in our approach, the resulting risk estimates accurately reflect uncertainties in the predicted radon exposure covariate. Posterior mean (95 per cent Bayesian credible interval) estimates of the relative risk associated with a 1 pCi/L increase in radon for ALL, AML, CLL, and CML are 0.91 (0.78-1.03), 1.01 (0.92-1.12), 1.06 (0.96-1.16), and 1.12 (0.98-1.27), respectively.     

Models for retrospective quantification of indoor radon exposure in case-control studies

In epidemiologic studies on lung cancer risk due to indoor radon the quantification of individual radon exposure over a long time period is one of the main issues. Therefore, radon measurements in one or more dwellings, which in total have been inhabited by the participants for a sufficient time-period, are necessary as well as consideration of changes of building characteristics and ventilation habits, which influence radon concentration. Given data on 1-y alpha-track measurements and personal information from 6,000 participants of case-control studies in West and East Germany, an improved method is developed to assess individual radon exposure histories. Times spent in different rooms of the dwelling, which are known from a personal questionnaire, are taken into account. The time spent outside the house (average fraction 45%) varies substantially among the participants. Therefore, assuming a substantially lower radon exposure outside the dwelling, the residence time constitutes an important aspect of total radon exposure. By means of an analysis of variance, important determinants of indoor radon are identified, namely constant conditions such as type of house (one family house or multiple dwelling), type of construction (half-timbered, massive construction, lightweight construction), year of construction, floor and type of basement, and changeable conditions such as heating system, window insulation, and airing habits. A correction of measurements in former dwellings by factors derived from the analysis is applied if current living conditions differ from those of the participants at the time when they were living in the particular dwellings. In rare cases the adjustment for changes leads to a correction of the measurements with a factor of about 1.4, but a reduction of 5% on average only. Exposure assessment can be improved by considering time at home and changes of building and ventilation conditions that affect radon concentration. The major concern that changes in ventilation habits and building conditions lead to substantial errors in exposure (and therefore risk) assessment cannot be confirmed in the data analyzed.     

An improved model of a battery-powered aspirator

Detailed instructions are provided to modify a commercially available, battery-powered, leaf/grass blower into a portable, hand-held aspirator for collecting adult mosquitoes and other small dipterans. Directions are given also to convert paper cups into interchangeable collection containers for use with the aspirator.     

The exposure of United Kingdom miners to radon

Duggan, M.J., Soilleux, P.J., Strong, J.C., and Howell, D.M. (1970).Brit. J. industr. Med.,27, 106-109. The exposure of United Kingdom miners to radon. Airborne radon has been recognized as a probable cause of lung cancer since the epidemiological studies made in the mining communities of Schneeberg and Jachymov during the 1920s and 1930s. Uranium miners are generally exposed to high concentrations of radon, and the growth of the uranium mining industry in the past 20 years has therefore stimulated a great amount of work on the risk from inhalation of radon and its daughters. However, there is still no general agreement on either the physical measurements in which the maximum permissible concentration in air should be expressed or the numerical value of this concentration.

There are no uranium mines being worked in the United Kingdom but there are considerable numbers of coal and other mines. It was therefore decided to make some radon measurements in a selection of mines in the UK to see if there was any prospect of obtaining useful dose-risk data. Measurements were made in 22 mines in all - 12 coal mines and 10 other mines - and the highest concentrations were found in three haematite mines in West Cumberland and in the two tin mines which were visited. The concentrations in these five mines were, in general, greater than 0·3 of a working level (WL) and in many locations were greater than 1 WL.

Because of these findings and also because an excess incidence of lung cancer among West Cumberland haematite miners has been previously reported, a further study of the mortality experience of West Cumberland miners has been carried out by Boyd, Doll, Faulds, and Leiper (1970). Their findings are reported in this Journal (p. 97).

     

Adult myeloid leukaemia and radon exposure: a Bayesian model for a case-control study with error in covariates

The possible association between radon exposure in dwellings and adult myeloid leukaemia had been explored in an Italian province by a case-control study. A total of 44 cases and 211 controls were selected from death certificates file. No association had been found in the original study (OR = 0.58 for > 185 vs 80 < or = Bq/cm). Here we reanalyse the data taking into account the measurement error of radon concentration and the presence of missing data. A Bayesian hierarchical model with error in covariates is proposed which allows appropriate imputation of missing values.The general conclusion of no evidence of association with radon does not change, but a negative association is not observed anymore (OR = 0.99 for > 185 vs 80 < or = Bq/cm). After adjusting for residential house radon and gamma radiation, and for the multilevel data structure, geological features of the soil is associated with adult myeloid leukaemia risk (OR = 2.14, 95 per cent Cr.I. 1.0-5.5).     

An improved CML estimation procedure for the Rasch model with item response data

Ordinal response data are commonly observed in health and medical investigations that include several items. The primary goal in the modelling of item response data is to find a unique measurement of the person's abilities and of the item difficulties that satisfies the properties of the fundamental measurement. One such analytic method in item response theory is the Rasch measurement, which is a way to convert ordinal observations into linear measures. Current estimation strategies assume the independence of the Rasch model parameters. In this paper, based on the conditional maximum likelihood, we implemented a simultaneous estimation method that can compare the Rasch parameters more efficiently. We also obtained the asymptotic properties of these estimators and developed the conditional likelihood ratio test for the goodness-of-fit of the model. Simulation studies were used to demonstrate the improved performance of our estimators as compared to that of currently used conditional method known as the CON procedure. We conclude that our estimation method outperforms CON in both model fit and the precision of the Rasch estimators.     

An index of past asbestos exposure as applied to car and bus mechanics

Different ways to describe historic fibre exposure from asbestos-containing friction materials were studied and compared for a group of 103 car and bus mechanics with more than 20 years employment and 15 years of asbestos exposure. A model was constructed to calculate cumulative asbestos exposure from friction materials including duration, intensity and exposure last year. The model is a combination of an additive and a multiplicative model, where an asbestos index was constructed that takes both near field and far field exposure into consideration. The model was based upon data from the international literature and quantitative asbestos measurements performed 1976–1988 in Swedish car repair workshops. The fibres were counted by phase-contrast microscopy with fibre criteria of length >5 μm and aspect ratio ≥3:1. The mechanics' fibre exposure at 398 repair workshops during a period of 48 years were calculated using the model. The mean cumulative exposure was estimated to be 2.6 f ml⁻¹1 year. The annual cumulative exposure was highest for truck mechanics in the early 1960s. The car mechanics had a time-weighted average fibre exposure range of 0.11 – 0.41 f ml⁻¹ (mean 0.21 f ml⁻¹) in 1965 compared to 0.003 – 0.08 f ml⁻¹ (mean 0.021 f ml⁻¹ in 1985. In order to validate the model, the mechanics' fibre exposure estimated using the model were compared with representative asbestos exposure measurements for car mechanics during the 1960s and the 1970s (correlation coefficient = 0.69). Five lung physiological variables (FVC, TLC, FEV₁, TL_co and CV%) were used to study exposure-response relationships. None of the exposure parameters suggested any significant relationship between exposure and decrease in lung function.     

An improved environmental pathway model for assessing high-level waste repository risks

An environmental pathway model useful for assessing the postclosure radiological risks from high-level waste repositories has been developed. The model describes more fully than its predecessors the long-term build-up of radionuclides in the biosphere and is consequently better suited to the analysis of the prolonged radionuclide releases potentially associated with geologic waste repositories. The effect of incorporating the additional features is to alter, in some cases substantially, the predicted population risks associated with a given long-term release of particular radionuclides. The model has been used to evaluate certain assumptions underlying the environmental standard for high-level waste repositories recently issued by the U.S. Environmental Protection Agency.     

Meta-analysis of residential exposure to radon gas and lung cancer

OBJECTIVES: To investigate the relation between residential exposure to radon and lung cancer. METHODS: A literature search was performed using Medline and other sources. The quality of studies was assessed. Adjusted odds ratios with 95% confidence intervals (CI) for the risk of lung cancer among categories of levels of exposure to radon were extracted. For each study, a weighted log-linear regression analysis of the adjusted odds ratios was performed according to radon concentration. The random effect model was used to combine values from single studies. Separate meta-analyses were performed on results from studies grouped with similar characteristics or with quality scores above or equal to the median. FINDINGS: Seventeen case-control studies were included in the meta-analysis. Quality scoring for individual studies ranged from 0.45 to 0.77 (median, 0.64). Meta-analysis based on exposure at 150 Bq/m3 gave a pooled odds ratio estimate of 1.24 (95% CI, 1.11-1.38), which indicated a potential effect of residential exposure to radon on the risk of lung cancer. Pooled estimates of fitted odds ratios at several levels of randon exposure were all significantly different from unity--ranging from 1.07 at 50 Bq/m3 to 1.43 at 250 Bq/m3. No remarkable differences from the baseline analysis were found for odds ratios from sensitivity analyses of studies in which > 75% of eligible cases were recruited (1.12, 1.00-1.25) and studies that included only women (1.29, 1.04-1.60). CONCLUSION: Although no definitive conclusions may be drawn, our results suggest a dose-response relation between residential exposure to radon and the risk of lung cancer. They support the need to develop strategies to reduce human exposure to radon.