Biomedical subjects

P N Price

Publications and source records attributed to P N Price.

9 recordsLinked to original sources

PubMed2004

Worker performance and ventilation in a call center: analyses of work performance data for registered nurses.

UNLABELLED: We investigated the relationship between ventilation rates and individual work performance in a call center, and controlled for other factors of the indoor environment. We randomized the position of the outdoor air control dampers, and measured ventilation rate, differential (indoor minus outdoor) carbon dioxide (DeltaCO(2)) concentration, supply air velocity, temperature, humidity, occupant density, degree of under-staffing, shift length, time of day, and time required to complete two different work performance tasks (talking with clients and post-talk wrap-up to process information). DeltaCO(2) concentrations ranged from 13 to 611 p.p.m. We used multivariable regression to model the association between the predictors and the responses. We found that agents performed talk tasks fastest when the ventilation rate was highest, but that the relationship between talk performance and ventilation was not strong or monotonic. We did not find a statistically significant association between wrap-up performance and ventilation rate. Agents were slower at the wrap-up task when the temperature was high (> 25.4 degrees C). Agents were slower at wrap-up during long shifts and when the call center was under-staffed. PRACTICAL IMPLICATIONS: The productivity benefits of ventilation rates that exceed common standards such as ASHRAE Standard 62 may be small (0-2%), and other factors may have a larger impact on productivity. Understaffing and long shifts should be avoided because both showed a negative impact on performance. In this study, high temperature had the largest statistically significant impact on productivity and was caused by occupants fighting over the thermostat setpoint. Care should be taken to avoid high temperatures in call centers. If occupants are allowed to adjust temperature setpoints, then the size and/or duration of the setpoint change should be restricted.

Humans↗

PubMed1999

All maps of parameter estimates are misleading.

Maps are frequently used to display spatial distributions of parameters of interest, such as cancer rates or average pollutant concentrations by county. It is well known that plotting observed rates can have serious drawbacks when sample sizes vary by area, since very high (and low) observed rates are found disproportionately in poorly-sampled areas. Unfortunately, adjusting the observed rates to account for the effects of small-sample noise can introduce an opposite effect, in which the highest adjusted rates tend to be found disproportionately in well-sampled areas. In either case, the maps can be difficult to interpret because the display of spatial variation in the underlying parameters of interest is confounded with spatial variation in sample sizes. As a result, spatial patterns occur in adjusted rates even if there is no spatial structure in the underlying parameters of interest, and adjusted rates tend to look too uniform in areas with little data. We introduce two models (normal and Poisson) in which parameters of interest have no spatial patterns, and demonstrate the existence of spatial artefacts in inference from these models. We also discuss spatial models and the extent to which they are subject to the same artefacts. We present examples from Bayesian modelling, but, as we explain, the artefacts occur generally.

Bayes Theorem↗

PubMed1997

Predictions and maps of county mean indoor radon concentrations in the mid-Atlantic states.

Measured surface radium content, geologic province information, information on the fraction of homes with basements and with living-area basements, and measurements from the EPA/State Residential Radon Surveys, were used in a Bayesian mixed effects regression to predict the distributions of short-term winter and annual living-area average radon concentrations by county in the mid-Atlantic states. The information provided by those explanatory variables is roughly equivalent to collecting an extra 12 observations per county, effectively doubling the amount of information in a typical county. Predicted county geometric means are subject to standard errors of 15% to 30% for typical counties, with the uncertainty in a given county depending on the number of radon measurements in the county and the amount of information about the geologic province that contains the county. After controlling for soil radium concentration and the effect of measuring in a basement vs. the first floor, typical geologic provinces are found to be associated with elevation or depression of indoor radon concentrations by 30% on average, with some provinces having effects of considerably larger magnitude.

Air Pollutants, Radioactive↗

PubMed1996

Bayesian prediction of mean indoor radon concentrations for Minnesota counties.

Past efforts to identify areas with higher than average indoor radon concentrations by examining the statistical relationship between local mean concentrations and physical parameters such as the soil radium concentration have been hampered by the variation in local means caused by the small number of homes monitored in most areas. In this paper, indoor radon data from a survey in Minnesota are analyzed to minimize the effect of finite sample size within counties, to determine the true county-to-county variation of indoor radon concentrations in the state, and to find the extent to which this variation is explained by the variation in surficial radium concentration among counties. The analysis uses hierarchical modeling, in which some parameters of interest (such as county geometric mean radon concentrations) are assumed to be drawn from a single population, for which the distributional parameters are estimated from the data. Extensions of this technique, known as random effects regression and mixed effects regression, are used to determine the relationship between predictive variables and indoor radon concentrations; the results are used to refine the predictions of each county's radon levels, resulting in a great decrease in uncertainty. The true county-to-county variation of geometric mean radon levels is found to be substantially less than the county-to-county variation of the observed geometric means, much of which is due to the small sample size in each county. The variation in the logarithm of surficial radium content is shown to explain approximately 80% of the variation of the logarithm of geometric mean radon concentration among counties. The influences of housing and measurement factors, such as whether the monitored home has a basement and whether the measurement was made in a basement, are also discussed. The statistical method can be used to predict mean radon concentrations, or applied to other geographically distributed environmental parameters.

Air Pollution, Indoor↗

PubMed1995

The regression effect as a cause of the nonlinear relationship between short- and long-term radon concentration measurements.

The relationship between four-day charcoal canister radon measurements and year-long alpha-track detector measurements in 983 New Jersey homes has been recently examined by others. The ratio of canister measurement to long-term measurement for the homes in the survey, a common parameter of interest, was found to increase as the canister measurement increased. The examination presented considerable discussion of the variation of the ratios as functions of various parameters. Although we did not examine the raw data used in the study, it appears that many of the results (and perhaps those in other papers) are consistent with a simple model in which both the long-term and rescaled short-term measurements provide measurements with error of the annual-average radon concentration in the home with no nonlinearity or other unusual functional dependence on radon concentration. We provide an example and discussion of this result, which is due to the widely known but frequently misunderstood phenomenon called "regression toward the mean," or simply the "regression effect." This does not invalidate the work of others; we merely wish to bring attention to the fact that the results in these papers may have a very simple explanation.

Radon↗

PubMed1990

Acrolein depletes the neuropeptides CGRP and substance P in sensory nerves in rat respiratory tract.

The mammalian respiratory tract is densely innervated by autonomic and sensory nerves around airways and blood vessels. Subsets of these nerves contain a number of putative neurotransmitter peptides, such as substance P and calcitonin gene-related peptide (CGRP) in sensory nerves and vasoactive intestinal polypeptide (VIP), possibly serving autonomic functions. CGRP is also found in endocrine cells in rat airway epithelium. These peptides are all pharmacologically potent effectors of bronchial and vascular smooth muscle and bronchial secretion. Their functions in vivo are less well established. We have therefore examined the effects of inhaled acrolein, a sensory irritant, on three pulmonary neuropeptides: CGRP, substance P, and VIP. Groups of rats (n = 3 each) were exposed for 10 min to acrolein in air (Ct = 510, 1858, and 5693 mg.min/m3) or to air alone. Fifteen minutes later they were killed (pentabarbitone IP) and their respiratory tracts were dissected and fixed in 0.4% p-benzoquinone solution. Cryostat sections were stained by indirect immunofluorescence for a general nerve marker (PGP 9.5) and neuropeptides. The acrolein-treated animals had a dose-related decrease in tracheal substance P- and CGRP-immunoreactive nerve fibers compared with controls. No change was seen in total nerve fiber distribution and number (PGP 9.5) or VIP immunoreactivity, nor in CGRP-immunoreactive epithelial endocrine cells. It is concluded that the rat tracheal peptidergic nerves are a sensitive indicator of inhaled irritant substances. Their reduced immunoreactivity may be because of a release of sensory neuropeptides that could play a role in the physiological response to irritant or toxic compounds.

Acrolein↗

PubMed1986

Acute toxicity of T2 mycotoxin to the guinea-pig by inhalation and subcutaneous routes.

The acute inhalation and subcutaneous toxicity of T2 mycotoxin has been investigated in guinea-pigs. The toxicity by the two routes was quantitatively and qualitatively similar. The LCt50 was 5749 mg min m-3 and the subcutaneous LD50 1-2 mg kg-1. Histological changes in the decedents which were similar by both routes of administration were most marked in the lymphoreticular system but also occurred in the gut. Lymphocytolysis and phagocytosis occurred in both the cortex of the thymus and of the lymph nodes. Lymph nodes were more severely affected in the decedents among the animals dosed with T2 by the subcutaneous route. The small intestine exhibited dead and dying cells throughout the lamina propria after T2 by either route.

Aerosols↗

PubMed1981

Oxygen consumption of human endometrium during the menstrual cycle measured in vitro using an oxygen electrode.

Oxygen consumption of human endometrial tissue was measured in vitro in air and high oxygen gas phases using an oxygen electrode. The oxygen consumption increased throughout the proliferative phase, peaking around ovulation and then decreasing during the secretory phase. This pattern persisted whether the oxygen consumption was expressed on a dry weight, DNA or protein basis. Storage of the tissue and mincing produced lower values of oxygen consumption.

Adolescent↗

PubMedDate not supplied

A method for quantifying artefacts in mapping methods illustrated by application to headbanging.

Maps of disease rates (and other quantities) often must contend with variance associated with variable population sizes and low incidence within spatial units. These characteristics can lead to substantial statistical noise that can mask underlying spatial variation. As Gelman and Price illustrated, most conventional mapping methods fail to address this problem, and in fact can introduce statistical artefacts; mapped quantities can show spatial patterns even when there are no spatial patterns in the underlying parameter of interest. Kafadar evaluated the performance of the headbanging algorithm for spatial smoothing (Tukey and Tukey, Hansen) for eliminating small scale variation and preserving edge structure. Here we perform a simulation study to investigate the artefacts of maps smoothed by unweighted and weighted headbanging. We find substantial artefacts that depend on the spatial structure of the statistical variation (for example, the spatial pattern of sample sizes) and on the details of the spatial distribution of geographic units. The methods used here could readily be adapted to study other spatial smoothers; we choose headbanging because (i) it is an important method used in practice, and (ii) its heavily computational nature is naturally studied using simulation (in contrast to the analytical methods used by Gelman and Price).

Artifacts↗