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Gabriel M Leung

Publications and source records attributed to Gabriel M Leung.

At least 19 recordsLinked to original sources
PubMed2007

Non-parametric estimation of the case fatality ratio with competing risks data: an application to Severe Acute Respiratory Syndrome (SARS).

For diseases with some level of associated mortality, the case fatality ratio measures the proportion of diseased individuals who die from the disease. In principle, it is straightforward to estimate this quantity from individual follow-up data that provides times from onset to death or recovery. In particular, in a competing risks context, the case fatality ratio is defined by the limiting value of the sub-distribution function, F(1)(t) = Pr(T infinity, where T denotes the time from onset to death (J = 1) or recovery (J = 2). When censoring is present, however, estimation of F(1)(infinity) is complicated by the possibility of little information regarding the right tail of F(1), requiring use of estimators of F(1)(t(*)) or F(1)(t(*))/(F(1)(t(*))+F(2)(t(*))) where t(*) is large, with F(2)(t) = Pr(T <or=t and J = 2) being the analogous sub-distribution function associated with recovery. With right censored data, the variability of such estimators increases as t(*) increases, suggesting the possibility of using estimators at lower values of t(*) where bias may be increased but overall mean squared error be smaller. These issues are investigated here for non-parametric estimators of F(1) and F(2). The ideas are illustrated on case fatality data for individuals infected with Severe Acute Respiratory Syndrome (SARS) in Hong Kong in 2003.

Computer Simulation↗
PubMed2006

Horizontal equity in health care utilization evidence from three high-income Asian economies.

This paper compares the extent to which the principle of "equal treatment for equal need"(ETEN) is maintained in the health care delivery systems of Hong Kong, South Korea and Taiwan. Deviations in the degree to which health care is distributed according to need are measured by an index of horizontal inequity. Income-related inequality in utilization is split into four major sources: (i) direct effect of income; (ii) need indicators (self-assessed health status, activity limitation, and age and gender interaction terms); (iii) non-need variables (education, work status, private health insurance coverage, employer-provided medical benefits, Medicaid status (low-income medical assistance), geographic region and urban/rural residency and (iv) a residual term. Service types studied include western doctor, licensed traditional medicine practitioner (LTMP), dental and emergency room (ER) visits, as well as inpatient admissions. Violations of the ETEN principle are observed for physician and dental services in Hong Kong . There is pro-rich inequity in western doctor visits. Unusually, this inequity exists for general practitioner but not specialist care. In contrast, South Korea appears to have almost comprehensively maintained ETEN although the better-off have preferential access to higher levels of outpatient care. Taiwan shows intermediate results in that the rich are marginally more likely to use outpatient services, but quantities of western doctor and dental visits are evenly distributed while there is modest pro-rich bias in the number of LTMP episodes. ER visits and inpatient admissions in Taiwan are either proportional or slightly pro-poor. Future work should focus on the evaluation of policy interventions aimed at reducing the observed unequal distributions.

Asia↗
PubMed2006

Methods for monitoring influenza surveillance data.

BACKGROUND: A variety of Serfling-type statistical algorithms requiring long series of historical data, exclusively from temperate climate zones, have been proposed for automated monitoring of influenza sentinel surveillance data. We evaluated three alternative statistical approaches where alert thresholds are based on recent data in both temperate and subtropical regions. METHODS: We compared time series, regression, and cumulative sum (CUSUM) models on empirical data from Hong Kong and the US using a composite index (range = 0-1) consisting of the key outcomes of sensitivity, specificity, and time to detection (lag). The index was calculated based on alarms generated within the first 2 or 4 weeks of the peak season. RESULTS: We found that the time series model was optimal in the Hong Kong setting, while both the time series and CUSUM models worked equally well on US data. For alarms generated within the first 2 weeks (4 weeks) of the peak season in Hong Kong, the maximum values of the index were: time series 0.77 (0.86); regression 0.75 (0.82); CUSUM 0.56 (0.75). In the US data the maximum values of the index were: time series 0.81 (0.95); regression 0.81 (0.91); CUSUM 0.90 (0.94). CONCLUSIONS: Automated influenza surveillance methods based on short-term data, including time series and CUSUM models, can generate sensitive, specific, and timely alerts, and can offer a useful alternative to Serfling-like methods that rely on long-term, historically based thresholds.

Algorithms↗
PubMed2006

Comparison between empirical prokinetics, Helicobacter test-and-treat and empirical endoscopy in primary-care patients presenting with dyspepsia: a one-year study.

AIM: To investigate the optimal strategy to treat dyspeptic patients in primary care. METHODS: Dyspeptic patients presenting to primary care outpatient clinics were randomly assigned to: (1) empirical endoscopy, (2) H pylori test-and-treat, and (3) empirical prokinetic treatment with cisapride. Early endoscopy was arranged if patients remained symptomatic after 2 wk. Symptom severity, quality-of-life (SF-36) as well as patient preference and satisfaction were assessed. All patients underwent endoscopy by wk 6. Patients were followed up for one year. RESULTS: Two hundred and thirty four patients were recruited (163 female, mean age 49). 46% were H pylori positive. 26% of H pylori tested and 25% of empirical prokinetic patients showed no improvement at wk 2 follow-up and needed early endoscopy. 15% of patients receiving empirical cisapride responded well to treatment but peptic ulcer was the final diagnosis. Symptom resolution and quality-of-life were similar among the groups. Costs for the three strategies were HK dollar 4343, dollar 1771 and dollar 1750 per patient. 66% of the patients preferred to have early endoscopy. CONCLUSION: The three strategies are equally effective. Empirical prokinetic treatment was the least expensive but peptic ulcers may be missed with this treatment. The H pylori test-and-treat was the most cost-effective option.

Adolescent↗
PubMed2006

Obesity, physical activity, and mortality in a prospective chinese elderly cohort.

BACKGROUND: In older people, it is unclear whether obesity relates to mortality, which calls into question its etiologic role in disease and its public health relevance. This apparent lack of relationship in older people could be an artifactual result of their diverse health states. METHODS: We used Cox regression analysis to determine whether the effect of body mass index (BMI) (calculated as weight in kilograms divided by the square of height in meters) or physical activity on mortality varied with health status in a prospective cohort study of Chinese people 65 years or older enrolled from 1998 to 2000 at all of the 18 Elderly Health Centers of the Hong Kong Government Department of Health. Health status was categorized into 5 morbidity groups using a 12-item index covering illnesses, medications, frailty, and smoking. RESULTS: After a mean follow-up of 4.1 years, there were 3819 deaths in 54 088 subjects (96.5% successful follow-up). The effect of BMI on mortality varied with baseline health status (P<.001). In the healthiest group, obese people (BMI >/=25) had higher mortality (adjusted hazard ratio [HR], 1.54; 95% confidence interval [CI], 1.02-2.33), but in the unhealthiest group they had lower mortality (HR, 0.55; 95% CI, 0.49-0.63) compared with subjects of normal weight. Daily physical activity was associated with lower mortality compared with inactivity in the unhealthiest group (HR, 0.70; 95% CI, 0.61- 0.81) but not in the healthiest group. CONCLUSIONS: In the elderly, the relationship between obesity and mortality varies according to the underlying health status. In those with poor health status, obesity is associated with better outcome, whereas in those with initially good health status, obesity is associated with worse outcome.

Aged↗
PubMed2006

Clinical prognostic rules for severe acute respiratory syndrome in low- and high-resource settings.

BACKGROUND: An accurate prognostic model for patients with severe acute respiratory syndrome (SARS) could provide a practical clinical decision aid. We developed and validated prognostic rules for both high- and low-resource settings based on data available at the time of admission. METHODS: We analyzed data on all 1755 and 291 patients with SARS in Hong Kong (derivation cohort) and Toronto (validation cohort), respectively, using a multivariable logistic scoring method with internal and external validation. Scores were assigned on the basis of patient history in a basic model, and a full model additionally incorporated radiological and laboratory results. The main outcome measure was death. RESULTS: Predictors for mortality in the basic model included older age, male sex, and the presence of comorbid conditions. Additional predictors in the full model included haziness or infiltrates on chest radiography, less than 95% oxygen saturation on room air, high lactate dehydrogenase level, and high neutrophil and low platelet counts. The basic model had an area under the receiver operating characteristic (ROC) curve of 0.860 in the derivation cohort, which was maintained on external validation with an area under the ROC curve of 0.882. The full model improved discrimination with areas under the ROC curve of 0.877 and 0.892 in the derivation and validation cohorts, respectively. CONCLUSION: The model performs well and could be useful in assessing prognosis for patients who are infected with re-emergent SARS.

Adult↗
PubMed2006

A prospective study of stage of change for general health promotion action and health-related lifestyle practices among Chinese adults.

In a previous study we proposed the notion of general health promotion action (GHPA) defined as "a general intention and actual practices to take action aimed to promote health." GHPA is a subjective measure of health-promoting lifestyle which may reflect practices aimed to promote health and practices which are taken for non-health reasons but which nonetheless have health benefits. The present prospective study aimed to examine whether baseline stage of change for GHPA predicted health-related lifestyle practices at 24-month follow-up in a representative community-based cohort of 3129 Hong Kong Chinese adults. Overall, 37% of the subjects remained in the same stage, 43% had progressed to later stages, and 20% had regressed to earlier stages of change at follow-up. Baseline maintainers were the most likely to report desirable lifestyle practices at follow-up. They were significantly more likely to have exercised in the past month, consumed at least 2 portions of fruit a day, consumed at least 3 portions of vegetable a day, consumed at least 5 portions of fruit or vegetable a day, have had no episodes of binge drinking in the past month, and have had a dental examination at least once a year. The association remained significant after adjusting for age, gender, education, income and baseline level of respective lifestyle practices, with significantly increasing trends from precontemplation to maintenance stage. We conclude that the predictive validity of stage of change for GHPA was supported from these longitudinal findings, and further research on how GHPA can guide health promotion strategies is warranted.

Adolescent↗
PubMed2006

Hong Kong's health spending projections through 2033.

OBJECTIVE: To derive actuarial projection estimates of Hong Kong's total domestic health expenditure to the year 2033. METHODS: Disaggregating health expenditure by age, sex, unit cost and utilisation level, we estimated future health spending by projecting utilisation (by public/private, inpatient/outpatient care) to reflect demographic changes and associated increase in demand (from higher expectations and greater intensity of care), and then multiplying such by the projected unit costs (incorporating the impact of key cost drivers such as public expectations, technological changes and potential productivity gains) to obtain total expenditure estimates. RESULTS: The model was most sensitive to the excess health care price inflation rate, i.e. the annual price/cost growth of medical goods and services over and above per capita GDP growth. Population ageing and growth per se, without taking into account related technologic innovation for chronic conditions that particularly afflict older adults, contribute relatively little to overall spending growth. Given the model assumptions, it is possible to limit total health spending to below 10% of GDP by 2033, where the public share would gradually decline from the current 57% to between 46% and 49%. CONCLUSIONS: Expenditure control through global budgeting, technology assessment and demand-side constraints should be considered although their effectiveness remains inconclusive.

Adolescent↗
PubMed2006

Risk-stratified seroprevalence of severe acute respiratory syndrome coronavirus among children in Hong Kong.

BACKGROUND: Severe acute respiratory syndrome was relatively mild in children, and the incidence was significantly lower when compared with adults. Although previous seroepidemiological studies demonstrated that asymptomatic infection was uncommon among health care workers and adult contacts of patients with severe acute respiratory syndrome, it is unclear whether this would extend to the pediatric population. OBJECTIVE: The purpose of this study was to determine the seroprevalence of severe acute respiratory syndrome coronavirus among asymptomatic children living near Amoy Gardens (site of largest community outbreak of severe acute respiratory syndrome in Hong Kong) compared with a low-risk region where no community transmission occurred. METHODS: The study was conducted from September to October 2003. Target subjects living in the defined high-risk and low-risk areas were approached through the schools within the respective localities. We recruited 353 and 361 children, respectively, from the high-risk and low-risk areas and collected 3 to 5 mL of blood for severe acute respiratory syndrome coronavirus IgG antibody testing by immunofluorescence antibody assay and confirmation by neutralization test. Parents of all of the subjects who joined the study were contacted by telephone, and a standardized questionnaire was administered by a research nurse to collect information including sociodemographic data, history of severe acute respiratory syndrome coronavirus infection in the subjects and members of the household, history of contact with known cases of severe acute respiratory syndrome, presence of severe acute respiratory syndrome-like symptoms since onset of the severe acute respiratory syndrome epidemic, travel history of the child and his/her relatives within the 15 days before any such symptom onset, use of health service as a result of such symptoms, and whether there were deaths of relatives as a result of severe acute respiratory syndrome. RESULTS: Two (0.57%) of 353 asymptomatic children from the high-risk area were tested positive for severe acute respiratory syndrome coronavirus antibody compared with 0 of 361 in the low-risk region. None of the 14 children who lived in the high-risk area and had known contacts with severe acute respiratory syndrome patients were seropositive. CONCLUSIONS: As in adults, subclinical severe acute respiratory syndrome coronavirus infection was rare in children in the 2003 epidemic. The very low seroprevalence implies little or no population herd immunity to protect against future resurgence of severe acute respiratory syndrome.

Adolescent↗
PubMed2006

Influenza-associated hospitalization in a subtropical city.

BACKGROUND: The impact of influenza on morbidity and hospitalization in the tropics and subtropics is poorly quantified. Uniquely, the Hong Kong Special Administrative Region has computerized hospital discharge diagnoses on 95% of total bed days, allowing disease burden for a well-defined population to be accurately assessed. METHODS AND FINDINGS: Influenza-associated morbidity and hospitalization was assessed by Poisson regression models for weekly counts of hospitalizations in Hong Kong during 1996 to 2000, using proportions of positive influenza types A (H1N1 and H3N2) and B isolations in specimens sent for laboratory diagnosis as measures of influenza virus circulation. We adjusted for annual trend, seasonality, temperature, and relative humidity, as well as respiratory syncytial virus circulation. We found that influenza was significantly associated with hospitalization for acute respiratory disease (International Classification of Diseases version 9 codes [ICD9] 460-466 and 480-487) and its subcategory pneumonia and influenza (ICD9 480-487) for all age groups. The annual rates of excess hospitalization per 100,000 population for acute respiratory diseases for the age groups 0-14, 15-39, 40-64, 65-74, and 75+ were 163.3 (95% confidence interval [CI], 135-190), 6.0 (95% CI, 2.7-8.9), 14.9 (95% CI, 10.7-18.8), 83.8 (95% CI, 61.2-104.2), and 266 (95% CI, 198.7-330.2), respectively. Influenza was also associated with hospitalization for cerebrovascular disease (ICD9 430-438) for those aged over 75 y (55.4; 95% CI, 23.1-87.8); ischemic heart disease (ICD9 410-414) for the age group 40-64 y (5.3; 95% CI, 0.5-9.5) and over 75 y (56.4; 95% CI, 21.1-93.4); and diabetes mellitus (ICD9 250) for all age groups older than 40 y. CONCLUSIONS: Influenza has a major impact on hospitalization due to cardio-respiratory diseases as well as on cerebrovascular disease, ischemic heart disease, and diabetes mellitus in the tropics and subtropics. Better utilization of influenza vaccine during annual epidemics in the tropics will enhance global vaccine production capacity and allow for better preparedness to meet the surge in demand that is inevitable in confronting a pandemic.

Adult↗
PubMed2006

Diet synergies and mortality--a population-based case-control study of 32,462 Hong Kong Chinese older adults.

BACKGROUND: Food and drink are not consumed in isolation and can have complimentary effects enhancing or blocking the overall uptake of nutrients. We investigated how combinations of foods, drinks, and smoking affected mortality. Method Adjusted logistic regression was used to assess the joint effect of healthy foods, less healthy foods, smoking, and alcohol use on mortality in a case-control study of all Chinese adults aged 60 or over who died in 1998; 21,494 dead cases (81% of all registered deaths) and 10,968 live controls were included. RESULTS: There was a significant trend of increasing all-cause mortality risk with decreasing healthy food consumption (P < 0.001), and the increase in risk was significantly steeper for people with high intakes of less healthy food (P for interaction <0.001). There was a steeper risk from increasing less healthy food intake in ever-smokers and people not drinking tea regularly (P < 0.001), while the J-shaped relationship between alcohol and mortality differed in shape with level of less healthy food intake. CONCLUSION: Intake of some dietary items may modify the effect of others. An analysis framework explicitly recognizing complementary and potentially synergistic effects of food, drinks, and smoking could enhance our understanding of dietary epidemiology.

Aged↗
PubMed2006

Age- versus time-comparative self-rated health in Hong Kong Chinese older adults.

OBJECTIVES: The main objectives were to examine the relation between age-comparative (self vs others of same age) self-rated health (SRH) and time-comparative (self this year vs last year) SRH, and to evaluate which was more strongly associated with specific physical health problems. METHODS: Cross-sectional data on two SRH measures and various physical health problems from 18749 male and 37413 female clients aged 65 or over from 18 Elderly Health Centres in Hong Kong were analysed using logistic regression with adjustment for potential confounders. RESULTS: Men were more likely to report 'better' and less likely to report 'worse' SRH than women. 'Normal' was the most common option but the proportions choosing this decreased with age on both SRH measures. There was a fairly weak but statistically significant correlation between these two measures, with Kappa coefficients of 0.125 and 0.167 for men and women, respectively. For both men and women, there were significantly positive linear trends between age-comparative SRH options from 'better' to 'worse' and physical health problems, such as respiratory diseases, musculoskeletal diseases, any active chronic diseases, functional disability, depressive symptoms, taking medication regularly, and admission to hospital last year. However, for time-comparative SRH, those who rated 'normal' had the smallest odds ratios in all of the physical health problems above than those who rated 'better' or 'worse'. CONCLUSIONS: The two SRH measures correlated with each other weakly but significantly. Age-comparative SRH was linearly, and time-comparative SRH was curvilinearly associated with physical health problems.

Age Factors↗
PubMed2006

Empirical implications of response acquiescence in discrete-choice contingent valuation.

The use of discrete-choice contingent valuation (CV) to elicit individuals' preference, expressed as maximum willingness-to-pay (WTP), although primarily developed in environmental economics, has been popular in the economic evaluation of health and healthcare. However, a concern with this method is the potential for 'over-estimating' WTP values due to the presence of response acquiescence, or 'yea-saying' bias. Based on a CV survey conducted to estimate physicians' valuation of clinic computerization, the extent of such bias was estimated from a within-sample open-ended valuation question following the respondents' discrete choice response. Analysis of this data suggests that not only was response acquiescence an issue, but also that the parametric estimation of mean and median WTP, the most common approach to estimating WTP from discrete-choice data, would potentially magnify such bias (to various degrees depending on the distributional assumptions applied). The possible extent of CV design versus analysis in discrete-choice methods therefore warrants further exploration.

Choice Behavior↗
PubMed2006

Evidence-based medical education -quo vadis?

The evidence base for most educational initiatives, at least until very recently, is largely composed of low-level evidence. Four major barriers underlie this historical observation, namely: (1) perceived ethical and acceptability problems arising from the unequal treatment of learners in experimental designs; (2) limited choice of outcome measures and validated instruments; (3) time and resource constraints; and (4) methodological issues concerning contextual confounding and small sample sizes. We advocate the adoption of a 'balanced scorecard' approach in the evaluation of education interventions that brings together a comprehensive panel of outcomes under one framework. We require a diversity of rigorously applied methods to generate these outcomes, drawing from the quantitative and qualitative disciplines of epidemiology, psychology and economics. We further suggest that the research community discuss and agree on a standardized set of common metrics or benchmarks. We conclude with a case study examining whether a hand-held computer clinical decision support tool improves clerkship learning of evidence-based medicine. The era of Brownian motion in health education research is over. What we demand in terms of burden of proof for educational effectiveness should be no less rigorous than our call for an ever escalating threshold concerning evidence of clinical care.

Benchmarking↗
PubMed2006

Age-period-cohort analysis of cervical cancer incidence in Hong Kong from 1972 to 2001 using maximum likelihood and Bayesian methods.

OBJECTIVE: To examine the secular effects of opportunistic screening for cervical cancer in a rich, developed community where most other such populations have long adopted organised screening. DESIGN, SETTING, AND PARTICIPANTS: The analysis was based on 15 140 cases of invasive cervical cancer from 1972 to 2001. The effects of chronological age, time period, and birth cohort were decomposed using both maximum likelihood and Bayesian methods. RESULTS: The overall age adjusted incidence decreased from 24.9 in 1972-74 to 9.5 per 100,000 in 1999-2001, in a log-linear fashion, yielding an average annual reduction of 4.0% (p<0.001) during the 30 year period. There were two second order and thus identifiable changes: (1) around the mid-1920s cohort curve representing an age-period interaction masquerading as a cohort change that denotes the first availability of Pap testing during the 1960s concentrated among women in their 40s; (2) a hook around the calendar years 1982-83 when cervical cytology became a standard screening test for pregnant women. CONCLUSIONS: Hong Kong's cervical cancer rates have declined since Pap tests first became available in the 1960s, most probably because of increasing population coverage over time and in successive generations in a haphazard fashion and punctuated by the systematic introduction of routine cytology as part of antenatal care in the 1980s.

Adult↗
PubMed2006

How evidence-based are publications in clinical ophthalmic journals?

PURPOSE: To evaluate the methodological quality and level of evidence of publications in four leading general clinical ophthalmology journals. METHODS: All 1919 articles published in the American Journal of Ophthalmology, Archives of Ophthalmology, British Journal of Ophthalmology, and Ophthalmology in 2004 were reviewed. The methodological rigor and the level of evidence in the articles were rated according to the McMaster Hedges Project criteria and the Oxford Centre for Evidence-Based Medicine levels of evidence. RESULTS: Overall, 196 (24.4%) of the 804 publications that were included for assessment met the Hedges criteria. Articles on economics evaluation and those on prognosis achieved the highest passing rate, with 80.0% and 74.4% of articles, respectively, meeting the Hedges criteria. Publications on etiology, diagnosis, and treatment fared less well, with respective passing rates of 28.3%, 20.2%, and 14.7%. Published systematic reviews and randomized controlled trials were uncommon in the ophthalmic literature, at least in these four journals during 2004. According to the Oxford criteria, 57.6% of the articles were classified as level 4 evidence compared with 18.1% classified as level 1. Articles on prognosis had the highest proportion (43.0%) rated as level 1 evidence. Generally, articles that reached the Hedges threshold were rated higher on the level-of-evidence scale (Spermans rho = 0.73; P < 0.001). CONCLUSIONS: The methodological quality of publications in the clinical ophthalmic literature was comparable to that in the literature of other specialties. There was substantial heterogeneity in quality between different types of articles. Future methodological improvements should focus on the areas identified as having the largest deficiencies.

Biomedical Research↗