Biomedical subjects

Karen Y Fung

Publications and source records attributed to Karen Y Fung.

7 recordsLinked to original sources

PubMed2007

A comparison of methods for the analysis of recurrent health outcome data with environmental covariates.

Recurrent events such as repeated hospital admissions for the same health outcome occur frequently in environmental health studies. Dewanji and Moolgavkar proposed a flexible parametric model and a conditional likelihood analysis for recurrent events based on a Poisson process formulation. In this paper, we examine the statistical properties of the Dewanji-Moolgavkar (DM) estimator of the risk of an adverse health outcome associated with environmental exposures based on recurrent event data using computer simulation. We also compare the DM approach with both case-crossover analysis for multiple observations and time series analysis when there are no subject-specific covariates. When using a correctly specified model, the DM method produced better estimates with respect to relative mean square error when each subject had constant or curved baseline intensity functions than it did when baseline intensities were increasing or decreasing in a linear fashion. For under-specified models, the DM method outperformed case-crossover analysis for decreasing straight line intensity functions, was outperformed by case-crossover analysis for increasing straight line intensity functions, and was roughly equivalent to case-crossover analysis for constant and curved intensity functions. Case-crossover analysis produced superior risk estimates more frequently than the other two methods in the cases considered here, especially for linear representations of the baseline intensities.

Aged↗

PubMed2006

Condensation and validation of a 4-item index of the Acne-QoL.

BACKGROUND: The 19-item Acne-QoL is a validated psychometric instrument designed for use in clinical trials. OBJECTIVE: The purpose of this study was to develop a condensed version of the Acne-QoL as an alternative measure of psychosocial impact for use in routine clinical practice. METHODS: Four condensed versions of the Acne-QoL were evaluated by regression analysis in a subset of 434 patients. The version with four items most broadly representative of acne-specific quality of life combined with a high level of correlation to Acne-QoL total score was selected for further validation in two different patient samples. RESULTS: The patient ranked condensation, representing items from each domain of greatest patient-perceived importance and relevance was selected for further analysis (Acne-Q(4)). The Acne-Q(4) explained 98.5% of the variation in total score of Acne-QoL. Validation of the Acne-Q(4) in a follow-up group and an independent subset of patients resulted in Pearson correlation coefficients of 0.967 (p<0.001). Construct validity of the Acne-Q(4) was confirmed by demonstrating a similar relationship as the Acne-QoL to acne severity. LIMITATIONS: There is less breadth and detail of QoL information in the Acne-Q(4) than in the Acne-QoL. The analysis relied on a total score for Acne-QoL, which the original developers did not validate. CONCLUSIONS: The Acne-Q(4) is accurately reflective of the parent instrument and may facilitate the psychometric evaluation of the impact of facial acne on patients in routine clinical practice by its practicality.

Acne Vulgaris↗

PubMed2006

Association between air pollution and multiple respiratory hospitalizations among the elderly in Vancouver, Canada.

Recurrent events, such as repeated hospital admissions for the same health outcome, occur frequently in environmental health studies. In this study, we conducted an analysis of data on repeated respiratory hospitalizations among the elderly in Vancouver, Canada, for the period of June 1, 1995, to March 31, 1999, using a new method proposed by (Dewanji and Moolgavkar 2000, 2002) for recurrent events, and compared it with some traditional methods. In particular, we assessed the impact of ambient gaseous (SO2, NO2, CO, and O3) and particulate pollutants (PM10, PM2.5, and PM10-2.5) as well as the coefficient of haze (CoH) on recurrent respiratory hospital admissions. Using the new procedure, significant associations were found between admissions and 3-day, 5-day, and 7-day moving averages of the ambient SO2 concentrations, with the strongest association observed at the 7-day lag (RR = 1.044, 95% CI: 1.018-1.070). We also found PM10-2.5 for 3-day and 5-day lag to be significant, with the strongest association at 5-day lag (RR = 1.020, 95% CI: 1.001-1.039). No significant associations with admission were found with current day exposure.

Aged↗

PubMed2005

Association of ambient air pollution with respiratory hospitalization in a government-designated "area of concern": the case of Windsor, Ontario.

This study is part of a larger research program to examine the relationship between ambient air quality and health in Windsor, Ontario, Canada. We assessed the association between air pollution and daily respiratory hospitalization for different age and sex groups from 1995 to 2000. The pollutants included were nitrogen dioxide, sulfur dioxide, carbon monoxide, ozone, particulate matter 10 microm in diameter (PM10), coefficient of haze (COH), and total reduced sulfur (TRS). We calculated relative risk (RR) estimates using both time-series and case-crossover methods after controlling for appropriate confounders (temperature, humidity, and change in barometric pressure). The results of both analyses were consistent. We found associations between NO2, SO2, CO, COH, or PM10 and daily hospital admission of respiratory diseases especially among females. For females 0-14 years of age, there was 1-day delayed effect of NO2 (RR = 1.19, case-crossover method), a current-day SO2 (RR = 1.11, time series), and current-day and 1- and 2-day delayed effects for CO by case crossover (RR = 1.15, 1.19, 1.22, respectively). Time-series analysis showed that 1-day delayed effect of PM10 on respiratory admissions of adult males (15-64 years of age), with an RR of 1.18. COH had significant effects on female respiratory hospitalization, especially for 2-day delayed effects on adult females, with RRs of 1.15 and 1.29 using time-series and case-crossover analysis, respectively. There were no significant associations between O3 and TRS with respiratory admissions. These findings provide policy makers with current risks estimates of respiratory hospitalization as a result of poor ambient air quality in a government designated "area of concern."

Adolescent↗

PubMed2003

Comparison of time series and case-crossover analyses of air pollution and hospital admission data.

BACKGROUND: Time series analysis is the most commonly used technique for assessing the association between counts of health events over time and exposure to ambient air pollution. Recently, case-crossover analysis has been proposed as an alternative analytical approach. While each technique has its own advantages and disadvantages, there remains considerable uncertainty as to which statistical methodology is preferable for evaluating data of this type. METHODS: The objective of this paper is to evaluate the performance of different variations of these two procedures using computer simulation. Hospital admission data were generated under realistic models with known parameters permitting estimates based on time series and case-crossover analyses to be compared with these known values. RESULTS: While accurate estimates can be achieved with both methods, both methods require some decisions to be made by the researcher during the course of the analysis. With time series analysis, it is necessary to choose the time span in the LOESS smoothing process, or degrees of freedom when using natural cubic splines. For case-crossover studies using either uni- or bi-directional control selection strategies, the choice of time intervals needs to be made. CONCLUSIONS: We prefer the times series approach because the best estimates of risk that can be obtained with time series analysis are more precise than the best estimates based on case-crossover analysis.

Air Pollutants↗

PubMed2002

Optimal designs for estimating the effective dose in developmental toxicity experiments.

Recent advances in risk assessment have led to the development of joint dose-response models to describe prenatal death and fetal malformation rates in developmental toxicity experiments. These models can be used to estimate the effective dose corresponding to a 5% excess risk for both these toxicological endpoints, as well as for overall toxicity. In this article, we develop optimal experimental designs for the estimation of the effective dose for developmental toxicity using joint Weibull dose-response models for prenatal death and fetal malformation. Based on an extended series of developmental studies, near-optimal designs for prenatal death, malformation, and overall toxicity were found to involve three dose groups: an unexposed control group, a high dose equal to the maximum tolerated dose, and a low dose above or comparable to the effective dose. The effect on the optimal designs of changing the number of implants and the degree of intra-litter correlation is also investigated. Although the optimal design has only three dose groups in most cases, practical considerations involving model lack of fit and estimation of the shape of the dose-response curve suggest that, in practice, suboptimal designs with more than three doses will often be preferred.

Abnormalities, Drug-Induced↗

PubMedDate not supplied

Air pollution and daily hospital admissions for cardiovascular diseases in Windsor, Ontario.

OBJECTIVE: To examine the role that ambient air pollution plays in exacerbating cardiovascular disease hospitalization in Windsor, Ontario. METHODS: The number of daily cardiac hospital admissions was obtained from all Windsor hospitals from April 1, 1995 to December 31, 2000 and linked to concentrations of ambient air pollutants and weather variables. The logarithm of daily counts of hospitalization was regressed on the levels of pollutants, after adjusting for seasonal, weekly cycles, and weather variables using time series analysis with natural splines as smoothing functions. RESULTS: Of all the pollutants considered, sulphur dioxide (SO2) had the strongest effect on cardiac hospitalization among the > or = 65 age group. The percentage increase in daily admission was 2.6% for current day sulphur dioxide level (95% CI: 0.5-6.4), 4.0% for 2-day mean level (95% CI: 0.1-6.9), and 5.6% (95% CI: 1.5-9.9) for 3-day mean level for an increase in interquartile range of 19.3 ppb. When particulate PM10 was included in the model, the contributing effect of sulphur dioxide remained significant for the > or = 65 age group for all three levels. CONCLUSIONS: Short-term effects of sulphur dioxide are associated significantly to daily cardiac hospital admissions for people > or = 65 years of age living in Windsor. Since Windsor is a border city, additional monitoring and assessment is recommended to determine if air quality and resultant health effects have deteriorated since traffic congestion at the border has increased following the events of September 11, 2001.

Adolescent↗