Biomedical subjects

K F Lam

Publications and source records attributed to K F Lam.

At least 19 recordsLinked to original sources

PubMed2006

Semi-parametric accelerated failure time regression analysis with application to interval-censored HIV/AIDS data.

This paper demonstrates a way to investigate a potentially non-linear relationship between an interval-censored response variable and a continuously distributed explanatory variable. A potentially non-linear effect of a continuous explanatory variable on the response is incorporated into an accelerated failure time model, forming a partial linear model. A sieve maximum likelihood estimator (MLE) is suggested to simultaneously estimate all the parameters. The sieve MLE is shown to be asymptotically efficient and normally distributed. Simulation studies show that the proposed estimators for the scale and regression parameters are robust and efficient, and the estimator for the non-linear function is able to capture the shape of a variety of smooth non-linear functions. The model is applied to observational HIV data, where the response variable is the time to suppression of HIV viral load after initiation of antiretroviral therapy, and baseline viral load is investigated as a potentially non-linear effect.

Anti-Retroviral Agents↗

PubMed2006

Bivariate poisson-poisson model of zero-inflated absenteeism data.

Bimodal distributions of counts with one mode at zero are often seen in medical research. In a health survey parents were asked the number of days their children missed their activities (Y(1)) and the number of days their children spent in bed (Y(2)) due to illness in the past four weeks. Both variables exhibited zero inflation. We consider a bivariate Poisson-Poisson regression model, in which the two variables are regarded as indicators of an unobserved health status variable. Based on this, we further develop a bivariate Poisson-Poisson model that constrains Y(1)>or=Y(2). It is often claimed that there is a critical window of growth and nutrition in foetal life and infancy during which subsequent health status is affected. It is not clear whether the claim is true and whether childhood growth matters more. We analyse the bivariate data in relation to weight-for-age in infancy and weight gain from infancy to age 7 years. The findings do not support the existence of a critical window in infancy. There is some indication that childhood weight gain might affect health status.

Absenteeism↗

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

Coexistence between colorectal cancer/adenoma and coronary artery disease: results from 1382 patients.

BACKGROUND: Common risk factors exist in colorectal neoplasia (cancer or adenoma) and coronary artery disease. AIM: To investigate in a retrospective study if there is coexistence of the two events in patients > OR =50 years. METHODS: Computer data on colonoscopies performed on symptomatic patients, the corresponding medical record and colonic histology in 1997-2000 were retrieved. History of coronary artery disease was recorded. To adjust for the factors of age and sex, bivariate logistic regression analysis was used to test for coexistence. RESULTS: 1382 patients were recruited. Colorectal neoplasia and history of coronary artery disease were present in 27% (373) and 12% (167) of patients, respectively. The mean age of patients was older in colorectal neoplasia+ (75 +/- 11 vs. 69 +/- 13 years, P < 0.0001) and in coronary artery disease+ (79 +/- 9 vs. 69 +/- 12 years, P < 0.0001) patients. Male was the predominant sex in colorectal neoplasia+: 33% vs. 22% (P < 0.0001), but not in coronary artery disease+ (P = 0.29). Colorectal neoplasia+ patients were more likely to have coronary artery disease+ [21.2% (79/373) vs. 8.8% (89/1098) (P < 0.0001)]. Bivariate logistic regression analysis showed strong association between the two events (OR: 2.12, 95% CI: 1.5, 3.0). CONCLUSION: There is strong coexistence of colorectal neoplasia and coronary artery disease, probably due to exposure to common risk factors.

Adenoma↗

PubMed2006

Multilevel modelling of clustered grouped survival data using Cox regression model: an application to ART dental restorations.

In some controlled clinical trials in dental research, multiple failure time data from the same patient are frequently observed that result in clustered multiple failure time. Moreover, the treatments are often delivered by more than one operator and thus the multiple failure times are clustered according to a multilevel structure when the operator effects are assumed to be random. In practice, it is often too expensive or even impossible to monitor the study subjects continuously, but they are examined periodically at some regular pre-scheduled visits. Hence, discrete or grouped clustered failure time data are collected. The aim of this paper is to illustrate the use of the Monte Carlo Markov chain (MCMC) approach and non-informative prior in a Bayesian framework to mimic the maximum likelihood (ML) estimation in a frequentist approach in multilevel modelling of clustered grouped survival data. A three-level model with additive variance components model for the random effects is considered in this paper. Both the grouped proportional hazards model and the dynamic logistic regression model are used. The approximate intra-cluster correlation of the log failure times can be estimated when the grouped proportional hazards model is used. The statistical package WinBUGS is adopted to estimate the parameter of interest based on the MCMC method. The models and method are applied to a data set obtained from a prospective clinical study on a cohort of Chinese school children that atraumatic restorative treatment (ART) restorations were placed on permanent teeth with carious lesions. Altogether 284 ART restorations were placed by five dentists and clinical status of the ART restorations was evaluated annually for 6 years after placement, thus clustered grouped failure times of the restorations were recorded. Results based on the grouped proportional hazards model revealed that clustering effect among the log failure times of the different restorations from the same child was fairly strong (corr(child)=0.55) but the effects attributed to the dentists could be regarded as negligible (corr(dentist)=0.03). Gender and the location of the restoration were found to have no effects on the failure times and no difference in failure times was found between small restorations placed on molars and non-molars. Large restorations placed on molars were found to have shorter failure times compared to small restorations. The estimates of the baseline parameters were increasing indicating increasing hazard rates from interval 1 to 6. Results based on the logistic regression models were similar. In conclusion, the use of the MCMC approach and non-informative prior in a Bayesian framework to mimic the ML estimation in a frequentist approach in multilevel modelling of clustered grouped survival data can be easily applied with the use of the software WinBUGS.

Adolescent↗

PubMed2006

Semiparametric analysis of zero-inflated count data.

Medical and public health research often involve the analysis of count data that exhibit a substantially large proportion of zeros, such as the number of heart attacks and the number of days of missed primary activities in a given period. A zero-inflated Poisson regression model, which hypothesizes a two-point heterogeneity in the population characterized by a binary random effect, is generally used to model such data. Subjects are broadly categorized into the low-risk group leading to structural zero counts and high-risk (or normal) group so that the counts can be modeled by a Poisson regression model. The main aim is to identify the explanatory variables that have significant effects on (i) the probability that the subject is from the low-risk group by means of a logistic regression formulation; and (ii) the magnitude of the counts, given that the subject is from the high-risk group by means of a Poisson regression where the effects of the covariates are assumed to be linearly related to the natural logarithm of the mean of the counts. In this article we consider a semiparametric zero-inflated Poisson regression model that postulates a possibly nonlinear relationship between the natural logarithm of the mean of the counts and a particular covariate. A sieve maximum likelihood estimation method is proposed. Asymptotic properties of the proposed sieve maximum likelihood estimators are discussed. Under some mild conditions, the estimators are shown to be asymptotically efficient and normally distributed. Simulation studies were carried out to investigate the performance of the proposed method. For illustration purpose, the method is applied to a data set from a public health survey conducted in Indonesia where the variable of interest is the number of days of missed primary activities due to illness in a 4-week period.

Biometry↗

PubMed2006

Why do primary care doctors undertake postgraduate diploma studies in a mixed private/public Asian setting?

OBJECTIVE: The aim of this study was to examine the reasons why primary care doctors undertake postgraduate diploma studies in a mixed private/public Asian setting. METHODS: Twenty four past or current postgraduate diploma students of the family medicine unit (FMU) of the University of Hong Kong participated in three focus group interviews. A structured questionnaire was constructed based on the qualitative data collected and was sent to 328 former applicants of postgraduate diploma studies at FMU. RESULTS: "Upgrading medical knowledge and skills" and "improving quality of practice" were two of the factors that most of the respondents considered to be significant in motivating them to undertake postgraduate diploma studies. "Time constraint" and "workload in practice" were however the most significant demotivating factors. Financial issues were more seriously considered by the junior than the senior doctors. To be able to "expand patient base and/or number" was considered to be a significant factor by the private doctors who were also keen to "improve communication and relationship with patients". CONCLUSION: These findings suggest that there are mixed reasons for primary care doctors to undertake postgraduate diploma studies. Course organisers should take into consideration these various reasons in planning their programmes.

Adult↗

PubMed2005

Validated questionnaire on diagnosis and symptom severity for functional constipation in the Chinese population.

BACKGROUND: Functional constipation is a common problem in clinical practice. No validated questionnaire is available in Chinese. AIM: To develop a validated questionnaire for diagnosis and symptom assessment in functional constipation for the Chinese population. METHODS: One hundred and eleven patients with constipation and 110 healthy controls were presented with a 24-item constipation questionnaire in the Chinese language. Quality of life in constipation patients was assessed by Short Form-36. Polyethylene glycol was prescribed, for 4 weeks, to 20 patients with newly diagnosed constipation. The questionnaire was administered before and 4 weeks after treatment. Concept, content, construct, discriminant validity and reliability of the questionnaire were assessed. RESULTS: Six items were selected by logistic regression to account for most of the differences between controls and constipated patients with a good reproducibility and internal consistency. A cut-off score of > or =5 was determined to discriminate between controls and constipated patients with a sensitivity of 91% and a specificity of 91%. The constipation questionnaire correlated negatively with seven domains of the Short Form-36 and discriminated between constipated patients who reported symptomatic improvement during polyethylene glycol treatment. CONCLUSIONS: The Chinese constipation questionnaire could be used in epidemiological studies to assess the frequency and severity of constipation in patient populations and in interventional studies of constipation.

Adolescent↗

PubMed2005

Determinants of bone mineral density in Chinese men.

Osteoporotic fractures are increasing among Asian populations in both genders, but the risk factors for low bone mineral density (BMD) in Asian men is unclear. To determine the hormonal and lifestyle risk factors for low BMD in Asian men, we studied 407 community-dwelling southern Chinese men aged 50 years and above. Medical history and lifestyle habits were obtained with a structured questionnaire. Dietary calcium and phytoestrogen intake were assessed by a semi-quantitative questionnaire. BMD at the spine and hip were measured by dual-energy X-ray absorptiometry (DXA). Fasting blood was analyzed for 25(OH)D, parathyroid hormone (PTH), total and bioavailable estradiol (bio-E) and testosterone (bio-T). The mean age of the cohort was 68.42+/-10.4 (50-96) years. In the linear regression model, weight, age, body mass index (BMI), bio-E, PTH, cigarette smoking and weight-bearing exercise were significant determinants of total hip BMD. Together they explained 55% of the total variance of hip BMD, with body weight being the most important determining factor. With age and weight adjustment, height, bio-T and flavonoid intake were identified as additional determinants of total hip BMD. Strategies to prevent bone loss and osteoporosis in Asian men should include lifestyle modification and maintenance of hormonal sufficiency.

Absorptiometry, Photon↗

PubMed2005

Estimating the proportion of cured patients in a censored sample.

There has been a recurring interest in modelling survival data which hypothesize subpopulations of individuals highly susceptible to some types of adverse events while other individuals are assumed to be at much less risk, like recurrence of breast cancer. A binary random effect is assumed in this article to model the susceptibility of each individual. We propose a simple multiple imputation algorithm for the analysis of censored data which combines a binary regression formulation for the probability of occurrence of an event, say recurrence of the breast cancer tumour, and a Cox's proportional hazards regression model for the time to occurrence of the event if it does. The model distinguishes the effects of the covariates on the probability of cure and on the time to recurrence of the disease. A SAS macro has been written to implement the proposed multiple imputation algorithm so that sophisticated programming effort can be rendered into a user-friendly application. Simulation results show that the estimates are reasonably efficient. The method is applied to analyse the breast cancer recurrence data. The proposed method can be modified easily to accommodate more general random effects other than the binary random effects so that the random effects not only affect the probability of occurrence of the event, but also the heterogeneity of the time to recurrence of the event among the uncured patients.

Algorithms↗

PubMed2005

A chain multinomial model for estimating the real-time fatality rate of a disease, with an application to severe acute respiratory syndrome.

It is well known that statistics using cumulative data are insensitive to changes. World Health Organization (WHO) estimates of fatality rates are of the above type, which may not be able to reflect the latest changes in fatality due to treatment or government policy in a timely fashion. Here, the authors propose an estimate of a real-time fatality rate based on a chain multinomial model with a kernel function. It is more accurate than the WHO estimate in describing fatality, especially earlier in the course of an epidemic. The estimator provides useful information for public health policy makers for understanding the severity of the disease or evaluating the effects of treatments or policies within a shorter time period, which is critical in disease control during an outbreak. Simulation results showed that the performance of the proposed estimator is superior to that of the WHO estimator in terms of its sensitivity to changes and its timeliness in reflecting the severity of the disease.

Epidemiologic Methods↗

PubMed2005

Bayesian analysis of clustered interval-censored data.

The recording of multiple interval-censored failure times is common in dental research. Modeling multilevel data has been a difficult task. This paper aims to use the Bayesian approach to analyze a set of multilevel clustered interval-censored data from a clinical study to investigate the effectiveness of silver diamine fluoride and sodium fluoride varnish in arresting active dentin caries in Chinese pre-school children. The time to arrest dentin caries on a surface was measured. A three-level random-effects Weibull regression model was used. Analysis was performed with WinBUGS. Results revealed a strong positive correlation (0.596) among the caries lesions' arrest times on different surfaces from the same child. The software WinBUGS made the above complicated estimation simple. In conclusion, the annual application of silver diamine fluoride on caries lesions, and caries removal before the application, were found to shorten the arrest time.

Bayes Theorem↗

PubMed2004

Onset and disappearance of reflux symptoms in a Chinese population: a 1-year follow-up study.

BACKGROUND: The natural history of gastro-oesophageal reflux disease in Asian population has not been studied before. AIM: To study the onset and disappearances of reflux symptoms over a 1-year period in the Chinese population. METHODS: A population-based telephone survey was performed in 2002 and repeated 1 year later. The change in prevalence rate, onset and disappearance of gastro-oesophageal reflux disease, and the change in diagnoses were assessed. Factors associated with the onset and disappearance of gastro-oesophageal reflux disease were studied. RESULTS: A total of 712 subjects completed the first and second survey. The annual, monthly and weekly prevalence of gastro-oesophageal reflux disease were 34.1%, 10.1% and 2.7% respectively. The onset rate (per 1000 person-year) and disappearance rate of any gastro-oesophageal reflux disease and frequent gastro-oesophageal reflux disease (> or = monthly symptoms) were 209, 40; and 395, 243 respectively. Forty-four percentage of gastro-oesophageal reflux disease subjects changed their diagnoses in 2003. By multiple logistic regression analysis, high anxiety score (OR: 1.2, 95% CI: 1.1-1.2) and higher educational level (OR: 2.7, 95% CI: 1.3-6.3) were associated with the onset of gastro-oesophageal reflux disease; while the frequency of acid regurgitation (OR: 0.35, 95% CI: 0.17-0.70) and use of antisecretory therapy (OR: 0.50, 95% CI: 0.28-0.89) were associated with the disappearance of gastro-oesophageal reflux disease. CONCLUSION: The prevalence of gastro-oesophageal reflux disease is stable over 1 year. Higher anxiety score and higher educational level were associated with the onset of gastro-oesophageal reflux disease, while lower frequency of reflux symptoms and infrequent use of antisecretory therapy were associated with the disappearance of gastro-oesophageal reflux disease in a Chinese population.

Adult↗

PubMed2004

Double-blind, randomized controlled study to assess the effects of lansoprazole 30 mg and lansoprazole 15 mg on 24-h oesophageal and intragastric pH in Chinese subjects with gastro-oesophageal reflux disease.

BACKGROUND: Previous studies have suggested that the acid secretory capacity of the Chinese population is lower than that of the Western population. AIM: To compare the effect of lansoprazole 30 mg and 15 mg once daily on the 24-h oesophageal and intragastric pH profiles in Chinese patients with gastro-oesophageal reflux disease. METHODS: Forty-four patients (male to female ratio, 27 : 17; mean age, 53 years; 55% with oesophagitis) with gastro-oesophageal reflux disease were randomized to receive lansoprazole 30 mg or 15 mg once daily for 4 weeks. Measurement of the 24-h oesophageal and intragastric pH, gastro-oesophageal reflux disease symptoms and quality of life was performed at baseline and during the last week of each dosing period. RESULTS: Lansoprazole 30 mg maintained an intragastric pH > 4 for 10.5 h vs. 9.6 h for lansoprazole 15 mg (P = 0.44). The percentage total time at oesophageal pH < 4 was similar for lansoprazole 30 mg and 15 mg (2.0% vs. 2.3%, P = 0.30). The proportion of patients with complete cure of heartburn and acid regurgitation and the quality of life assessment were similar for lansoprazole 30 mg and 15 mg. Both dosages of lansoprazole were well tolerated and the compliance was 100% in both groups. CONCLUSION: Lansoprazole dosages of 30 mg and 15 mg once daily provide a satisfactory decrease for oesophageal acid exposure and are equally effective for the treatment of gastro-oesophageal reflux disease in the Chinese population.

2-Pyridinylmethylsulfinylbenzimidazoles↗

PubMed2004

The first batch of graduates of a new medical curriculum in Asia: how their teachers see them.

OBJECTIVE: To examine teachers' views of the first batch of graduates of a revised medical curriculum in Asia. METHODS: A cross-sectional study using a structured questionnaire was carried out to obtain the views of all the clinical teachers involved in teaching final year students of the old curriculum in 2000-01 and the new curriculum in 2001-02 at the University of Hong Kong, which commenced curricular reform in 1997. RESULTS: Nearly 62% of respondents felt that better graduates were being produced with the new curriculum. The majority of them rated the new curriculum students better in nearly all the major goals of the new curriculum, such as self-directed learning initiative, problem solving skills, interpersonal skills and clinical performance in patient care. However, the core knowledge of the new curriculum students was of concern to some teachers. CONCLUSION: This study focused on the first complete cycle of a revised medical curriculum in Asia. Teachers' views of the new curriculum students were highly positive and they felt that better graduates were being produced.

Attitude↗

PubMed2003

Prevalence, clinical spectrum and health care utilization of gastro-oesophageal reflux disease in a Chinese population: a population-based study.

BACKGROUND: Population-based data on gastro-oesophageal reflux disease in Chinese are lacking. The prevalence, clinical spectrum and health care-seeking behaviour of subjects with gastro-oesophageal reflux disease were studied. METHODS: Ethnic Chinese (3605) were invited to participate in a telephone survey using a validated gastro-oesophageal reflux disease questionnaire and the Hospital Anxiety and Depression Scale. RESULTS: A total of 2209 subjects (58% female; mean age, 40.3 years) completed the interview. The annual, monthly and weekly prevalence rates of gastro-oesophageal reflux disease were 29.8%, 8.9% and 2.5%, respectively. Gastro-oesophageal reflux disease symptoms were associated with non-cardiac chest pain [odds ratio (OR), 2.3; 95% confidence interval (95% CI), 1.7-3.1], dyspepsia (OR, 1.9; 95% CI, 1.4-2.5), globus (OR, 1.8; 95% CI, 1.2-2.7), acid feeling in the stomach (OR, 5.8; 95% CI, 4.5-7.5) and the use of non-steroidal anti-inflammatory drugs (OR, 2.3; 95% CI, 1.5-3.6), but not with dysphagia, bronchitis, asthma, hoarseness and pneumonia. Patients with gastro-oesophageal reflux disease had a significantly higher anxiety and depression score and required more days off work when compared with subjects without. The frequency of heartburn (P = 0.032), female gender (P < 0.001), degree of depression (P = 0.004) and social morbidity (P < 0.001) were independent factors associated with health care-seeking behaviour. CONCLUSION: The prevalence of gastro-oesophageal reflux disease was lower than that in Western populations, but carried a significant socio-economic burden in the studied Chinese population. The frequency of heartburn, female gender and psychosocial factors were associated with health care utilization in gastro-oesophageal reflux disease.

Adult↗

PubMed2003

REML and ML estimation for clustered grouped survival data.

Clustered grouped survival data arise naturally in clinical medicine and biological research. For example, in a randomized clinical trial, the variable of interest is the time to occurrence of a certain event with or without a new treatment and the data are collected from possibly correlated subjects from independent clusters. However it is sometimes impossible or too expensive to monitor the experimental subjects continuously. The subjects are examined regularly and the continuous survival data are thus grouped into a discrete time scale. With such a design, researchers are mainly interested in the effectiveness of the new treatment as well as the correlation among subjects from the same cluster, namely the intracluster correlation. This paper suggests a random effects approach to the estimation of the regression parameter with various choices of regression model and also the dependence parameter which characterizes the intracluster correlation. Time dependent covariates can be accommodated in the proposed model, and the estimation procedure will not be further complicated with large cluster sizes. The proposed method is applied to the data from the Diabetic Retinopathy Study, the objective of which is to evaluate the effectiveness of laser photocoagulation in delaying or preventing the onset of blindness in the left and right eyes of individuals with diabetes-associated retinopathy. The intracluster correlation using a grouped proportional hazards regression model can be estimated and the relationship between the regression parameter estimates based on the random effects approach and the marginal approach using a dynamic logistic regression model are discussed. Results from a simulation study of the proposed method are also presented.

Cluster Analysis↗

PubMed2003

A validated symptoms questionnaire (Chinese GERDQ) for the diagnosis of gastro-oesophageal reflux disease in the Chinese population.

BACKGROUND AND AIMS: To develop a validated gastro-oesophageal disease (GERD) symptom questionnaire for the Chinese population. METHODS: One hundred Chinese patients with GERD and 101 healthy Chinese controls were presented with a 20-item GERD questionnaire in the Chinese language (Chinese GERDQ). Quality of life in GERD patients was assessed by SF-36. A standard dose of proton pump inhibitors for 4 weeks was prescribed to 35 patients with newly diagnosed GERD. The Chinese GERDQ was performed before, 4 weeks and 8 weeks after treatment. Concept, content, construct, discriminant validity and reliability of the questionnaire were assessed. RESULTS: Seven items were selected by logistic regression to account for most of the differences between controls and GERD patients with a good reproducibility and internal consistency. A cut-off score of equal or greater than 12 was determined to discriminate between controls and GERD patients with a sensitivity of 82% and a specificity of 84%. The Chinese GERDQ correlated negatively with five domains of the SF-36 and discriminated between GERD patients who reported symptomatic improvement during proton pump inhibitor treatment and symptoms deterioration upon withdrawal of proton pump inhibitor treatment. CONCLUSIONS: The Chinese GERDQ could be used in epidemiological studies to assess the frequency and severity of GERD in patient populations and in interventional studies of GERD.

China↗