Development of multistage distillation in a microfluidic chip

Although there has been a lot of work on the development of microchemical processing systems such as micro-reactors and micro-sensors, little attention has been paid to micro-separation units, and in particular, microscale distillation. In this paper, various silicon-glass microscale distillation chips with different channel configurations were fabricated and tested. A temperature gradient was setup across the chip by heating and cooling the two ends. The feed was located at the middle of the microchannel. Arrays of micropillars were incorporated in order to guide the liquid flow. It was found that the separation performance was promoted by increasing the length of the microchannel. However, this created an imbalance of the liquid flows at the two sides of the microchannel and caused flooding. This hydrodynamic limitation was addressed by incorporating micropillars on both sides of the channel. The most efficient microdistillation chip consisted of a microchannel with 600 microns width and 40 cm length. Experimental results showed high efficiency for the separation of a 50 mol% acetone-water mixture when the heating and cooling temperature were 95 °C and 42 °C respectively. The concentrations of acetone were 3 mol% in the bottom stream and 95 mol% in the distillate, which was equivalent to at least 4 equilibrium stages at total reflux conditions. Furthermore, a 50 mol% methanol-toluene mixture was separated into nearly pure toluene in the bottom stream and 75 mol% methanol in the distillate. The performance of the microdistillation unit was reproducible in repeated tests.

Increased arterial stiffness in patients with psoriasis is associated with active systemic inflammation

BACKGROUND

Psoriasis is associated with premature atherosclerosis although the underlying mechanism remains unclear.

OBJECTIVES

We sought to investigate the relationship between disease activity and systemic inflammation in patients with psoriasis, and macrovascular and microvascular function.

METHODS

Fifty-two patients with psoriasis (mean ± SD age 44 ± 8 years; 38 men) were compared with 50 age- and sex-matched controls. Baseline demographics and high-sensitivity C-reactive protein (hs-CRP) level were recorded for each subject. Psoriatic disease activity was assessed using the Psoriasis Area and Severity Index (PASI). Arterial stiffness and endothelial function were assessed using brachial to ankle pulse wave velocity (baPWV) and digital hyperaemic response measured using the peripheral arterial tonometry (PAT) index.

RESULTS

Patients with psoriasis had significantly higher hs-CRP (mean ± SD 5·3 ± 5·1 vs. 1·9 ± 1·6 mg L(-1), P < 0·01) and baPWV (mean ± SD 14·5 ± 2·5 vs. 13·2 ± 1·6 m s(-1) , P < 0·01) but not PAT index (mean ± SD 2·06 ± 0·59 vs. 2·10 ± 0·44, P = 0·70) than controls. There was significant correlation of hs-CRP with baPWV (r = 0·51, P < 0·01) and with PASI (r = 0·48, P < 0·01). Multiple linear regression analysis demonstrated that baPWV is independently correlated with age, fasting glucose and hs-CRP (P < 0·05), but does not predict PAT index. Each mg L(-1) increase in hs-CRP accounted for an increase in baPWV of +0·12 m s(-1) (95% confidence interval 0·01-0·22, P = 0·03).

CONCLUSIONS

Young patients with psoriasis have increased arterial stiffness but not microvascular dysfunction compared with healthy controls. More importantly, hs-CRP positively correlated with, and independently predicted, arterial stiffness. This suggests that systemic inflammation in patients with psoriasis is associated with premature atherosclerosis.

Family medicine training in Hong Kong: similarities and differences between family and non-family doctors

OBJECTIVE

To study the local medical profession's opinions on the training requirements for the specialty of family medicine. This was to serve as a reference for future planning of the health care system.

DESIGN

Cross-sectional study.

PARTICIPANTS AND SETTING

All registered doctors in Hong Kong.

MAIN OUTCOME MEASURES

Doctors' ratings on the importance of vocational training, professional assessment, job nature, and experience to become suitably qualified as a family doctor, and their opinions on the length of necessary vocational training.

RESULTS

A total of 2310 doctors (23% of doctors in the local register) responded. Professional assessment was mostly agreed as a qualification, followed by vocational training, clinical experience, and job nature. Over 70% agreed on a training period of 4 years or less. Non-family doctors were more likely to opt for professional assessment as the qualification and also opt for a longer training period.

CONCLUSION

Vocational training was considered important as a qualification for the specialty of family medicine. The length of training was mostly agreed to be 4 years or less, not the 6 years currently required by the Hong Kong Academy of Medicine. The vocational training programme for family medicine might require re-examination.

Introducing family medicine in a pluralistic health care system: how patients and doctors see it

BACKGROUND

The health care systems in many countries are focused on specialist care. In those countries that have recently changed to a primary care-based system, some doctors and patients were dissatisfied with the change.

OBJECTIVE

To explore the opinions of the general public and the doctors on the change to a family medicine (FM)-based health care system.

METHODS

Qualitative study with focus groups of doctors working in different practice settings. Quantitative study with questionnaires sent to all doctors registered in Hong Kong and a telephone survey targeting the general public aged ≥18.

RESULTS

Doctors in the focus groups generally supported a FM-based health care system. They were concerned that there were not enough family doctors for such a system and the patients' current free choice of any doctor for primary care would impede its success. Thousand six hundred and forty-seven adults took part in the telephone survey (response rate 67.6%) and 2310 doctors (22.8%) responded to the questionnaire. Nearly 95% of the general public respondents agreed to the FM system though only 66.3% of them had ever heard of the term family doctor. About 65% of the doctors supported this system but only 33% agreed that the system would work. The specialist-doctors were less supportive of mandatory referral than the non-specialists, while the public was equally divided on this issue.

CONCLUSIONS

The public accepts the FM-based system but needs education on the benefits of primary health care. Direct access to the specialist would be the greatest barrier. Government involvements are essential for the reform.

Analysis of multilevel grouped survival data with time-varying regression coefficients

Correlated or multilevel grouped survival data are common in medical and dental research. Two common approaches to analyze such data are the marginal and the random-effects approaches. Models and methods in the literature generally assume that the treatment effect is constant over time. A researcher may be interested in studying whether the treatment effects in a clinical trial vary over time, say fade out gradually. This is of particular clinical value when studying the long-term effect of a treatment. This paper proposed to extend the random effects grouped proportional hazards models by incorporating the possibly time-varying covariate effects into the model in terms of a state-space formulation. The proposed model is very flexible and the estimation can be performed using the MCMC approach with non-informative priors in the Bayesian framework. The method is applied to a data set from a prospective clinical trial investigating the effectiveness of silver diamine fluoride (SDF) and sodium fluoride (NaF) varnish in arresting active dentin caries in the Chinese preschool children. It is shown that the treatment groups with caries removal prior to the topical fluoride applications are most effective in shortening the arrest times in the first 6-month interval, but their effects fade out rapidly since then. The effects of treatment groups without caries removal prior to topical fluoride application drop at a very slow rate and can be considered as more or less constant over time. The applications of SDF solution is found to be more effective than the applications of NaF vanish.

A simple approach to the estimation of incidence rate difference

The incidence rate difference (IRD) is a parameter of interest in many medical studies. For example, in vaccine studies, it is interpreted as the vaccine-attributable reduction in disease incidence. This is an important parameter, because it shows the public health impact of an intervention. The IRD is difficult to estimate for various reasons, especially when there are quantitative covariates or the duration of follow-up is variable. In this paper, the authors propose an approach based on weighted least-squares regression for estimating the IRD. It is very easy to implement because it boils down to performing ordinary least-squares regression analysis of transformed variables. Furthermore, if the outcome events are repeatable, the authors propose that data on all events be analyzed instead of first events only. Four versions of the Huber-White robust standard error are considered for statistical inference. Simulation studies are used to examine the performance of the proposed method. In a variety of scenarios simulated, the method provides an unbiased estimate for the IRD, and the empirical coverage proportion of the 95% confidence interval is very close to the nominal level. The method is illustrated with data from a vaccine trial carried out in the Gambia in 2001-2004.

Evaluation of the learning outcomes of a year-long postgraduate training course in community geriatrics for primary care doctors

There are increasing expectations on primary care doctors to shoulder a bigger share of care for patients with common geriatric problems in the community. This study aims to examine the outcomes of a postgraduate training course in geriatrics for primary care doctors. A questionnaire developed by the research team was sent to the course graduates (years 2001-2007). Ninety-eight replies were received with a response rate of 52.4% (98/187). Difference in the ratings by the respondents before and after taking the course was analyzed using the nonparametric Wilcoxon signed rank test. Most respondents felt more rewarding and had participated more in geriatric care, and the majority had improvement in their communication skills with elderly patients after taking the course. Moreover, the graduates are more confident in diagnosing and managing common geriatric problems, and deciding to which specialty to refer the elderly patients. Of the referrals, there was a significant increase to private geriatricians and a significant reduction to other specialists. The average number of elderly patients seen per day had also increased. However, little change was observed about making nursing home visits, the frequency of which remained low. Many graduates expressed difficulties in conducting nursing home visits.

Psychological well-being of interns in Hong Kong: what causes them stress and what helps them

BACKGROUND

Many doctors experience psychological ill health. Interns are known to be particularly vulnerable.

AIM

To examine the level of depression, anxiety and stress in interns in Hong Kong, as well as the causes and how they cope.

METHODS

A questionnaire was designed based on the themes identified in three focus groups of medical graduates of Year 2004 of the University of Hong Kong. The 21-item Depression, Anxiety and Stress Scale (DASS 21) was also administered. All 155 graduates of the same year were invited to participate with a response rate of 63%.

RESULTS

Percentages of respondents with abnormal levels of depression, anxiety and stress were 35.8%, 35.4% and 29.2%, respectively. Frequent calls during night shift, long working hours and heavy workload constituted the most significant stressors. Factor analysis of the stressors showed that seven factors could explain 68% of the total variance: multidisciplinary team working issues, clinical difficulties, job seeking and employment, workload issues, ethical and interpersonal issues, adjustment to job rotation and performance appraisal. Holidays, peers and sleep offered the most significant relief.

CONCLUSION

Interns experience considerable depression, anxiety and stress. The source of stress is multi-faceted, but workload is the most significant stressor. Peer support groups may relief stress.

Prevalence and extent of calcification over aorta, coronary and carotid arteries in patients with rheumatoid arthritis

OBJECTIVE

To evaluate the prevalence and pattern of arterial calcification in patients with rheumatoid arthritis (RA).

BACKGROUND

Patients with RA are prone to premature atherosclerosis; nonetheless the prevalence and extent of atherosclerosis in different vascular beds and their relationship to each other remain unknown.

METHODS

We studied the distribution and extent of arterial calcification in 85 RA patients and 85 age-and sex-matched controls. Arterial calcification as determined by calcium score (CS) were measured using multi-detector computed tomography in thoracic aorta, coronary and carotid arteries.

RESULTS

Compared with controls, RA patients had a significantly higher average CS and prevalence of CS > 0 in aorta, coronary and carotid arteries and overall arteries (all P < 0.05). After adjusting for age and sex, RA patients had a significantly higher relative risk of developing calcification in the aorta [Odds Ratio (OR) = 19.5, 95% Confidence Interval (CI): 8.0-47.6], followed by the carotid arteries (OR = 5.7, 95% CI:1.7-18.7) and coronary arteries (OR = 5.0, 95% CI:2.2-11.1) compared with controls (all P < 0.01). Amongst RA patients aged >60, 90% had diffuse arterial calcification, especially over the thoracic aorta, compared with 55% of controls who had arterial calcification clustered in the coronary arteries (P < 0.05). RA patients with total CS > 0 were older with a higher urea level and C-reactive protein than those without arterial calcification, no factor was found to be independently predictive for arterial calcification (all P > 0.05).

CONCLUSIONS

Our results demonstrated that RA patients had earlier onset, more diffuse arterial calcification over multiple vascular beds and more preferential involvement of thoracic aorta, rather than coronary artery when compared with control.

Iron supplement in pregnancy and development of gestational diabetes--a randomised placebo-controlled trial

OBJECTIVE

To test the hypothesis that iron supplement from early pregnancy would increase the risk of gestational diabetes mellitus (GDM).

DESIGN

Randomised placebo-controlled trial.

SETTING

A university teaching hospital in Hong Kong.

POPULATION

One thousand one hundred sixty-four women with singleton pregnancy at less than 16 weeks of gestation with haemoglobin (Hb) level between 8 and 14 g/dl and no pre-existing diabetes or haemoglobinopathies.

METHODS

Women were randomly allocated to receive 60 mg of iron supplement daily (n= 565) or placebo (n= 599). Oral glucose tolerance tests (OGTTs) were performed at 28 and 36 weeks. Women were followed up until delivery.

OUTCOME MEASURES

The primary outcome was development of GDM at 28 weeks. The secondary outcomes were 2-hour post-OGTT glucose levels, development of GDM at 36 weeks and delivery and infant outcomes.

RESULTS

There was no significant difference in the incidence of GDM in the iron supplement and placebo groups at 28 weeks (OR: 1.04, 95% confidence interval [CI]: 0.7-1.53 at 90% power) or 36 weeks. Maternal Hb and ferritin levels were higher in the iron supplement group at delivery (P < 0.001 and P= 0.003, respectively). Elective caesarean section rate was lower in the iron supplement group (OR: 0.58, 95% CI: 0.37-0.89). Infant birthweight was heavier (P= 0.001), and there were fewer small-for-gestational-age babies in the iron supplement group (OR: 0.46, 95% CI: 0.24-0.85).

CONCLUSION

Iron supplement from early pregnancy does not increase the risk of GDM. It may have benefits in terms of pregnancy outcomes.

Three estimates of the association between linear growth failure and cognitive ability

OBJECTIVES

To compare three estimators of association between growth stunting as measured by height-for-age Z-score and cognitive ability in children, and to examine the extent statistical adjustment for covariates is useful for removing confounding due to socio-economic status.

METHODS

Three estimators, namely random-effects, within- and between-cluster estimators, for panel data were used to estimate the association in a survey of 1105 pairs of siblings who were assessed for anthropometry and cognition. Furthermore, a 'combined' model was formulated to simultaneously provide the within- and between-cluster estimates.

RESULTS

Random-effects and between-cluster estimators showed strong association between linear growth and cognitive ability, even after adjustment for a range of socio-economic variables. In contrast, the within-cluster estimator showed a much more modest association: For every increase of one Z-score in linear growth, cognitive ability increased by about 0.08 standard deviation (P < 0.001). The combined model verified that the between-cluster estimate was significantly larger than the within-cluster estimate (P = 0.004).

CONCLUSION

Residual confounding by socio-economic situations may explain a substantial proportion of the observed association between linear growth and cognition in studies that attempt to control the confounding by means of multivariable regression analysis. The within-cluster estimator provides more convincing and modest results about the strength of association.

A test for constant fatality rate of an emerging epidemic: with applications to severe acute respiratory syndrome in Hong Kong and Beijing

The etiology, pathogenesis, and prognosis for a newly emerging disease are generally unknown to clinicians. Effective interventions and treatments at the earliest possible times are warranted to suppress the fatality of the disease to a minimum, and inappropriate treatments should be abolished. In this situation, the ability to extract most information out of the data available is critical so that important decisions can be made. Ineffectiveness of the treatment can be reflected by a constant fatality over time while effective treatment normally leads to a decreasing fatality rate. A statistical test for constant fatality over time is proposed in this article. The proposed statistic is shown to converge to a Brownian motion asymptotically under the null hypothesis. With the special features of the Brownian motion, we are able to analyze the first passage time distribution based on a sequential tests approach. This allows the null hypothesis of constant fatality rate to be rejected at the earliest possible time when adequate statistical evidence accumulates. Simulation studies show that the performance of the proposed test is good and it is extremely sensitive in picking up decreasing fatality rate. The proposed test is applied to the severe acute respiratory syndrome data in Hong Kong and Beijing.

Positive association between gastro-oesophageal reflux disease and irritable bowel syndrome in a Chinese population

BACKGROUND

Gastro-oesophageal reflux disease and irritable bowel syndrome are common diseases which may be related.

AIM

To examine the association between gastro-oesophageal reflux disease and irritable bowel syndrome in Chinese population in Hong Kong.

METHODS

Randomly selected ethnic Chinese were invited to participate in a telephone survey in 1996. Gastro-oesophageal reflux disease was defined as subjects having heartburn and/or acid regurgitation once weekly or more. Irritable bowel syndrome was diagnosed according to the Rome I criteria. The association between gastro-oesophageal reflux disease and irritable bowel syndrome was calculated using a statistical model which allows the odds ratio to be measured.

RESULTS

One thousand six hundred and forty-nine subjects completed the interview (response rate 62%). The population prevalence of gastro-oesophageal reflux disease and irritable bowel syndrome were 5% and 4%, respectively. Thirteen per cent of subjects with gastro-oesophageal reflux disease and 11% with irritable bowel syndrome suffered from both gastro-oesophageal reflux disease and irritable bowel syndrome. The OR of having gastro-oesophageal reflux disease and irritable bowel syndrome together was estimated to be 3 (95% CI: 1.05, 6.27) indicating a positive association between the two diseases. This association occurred predominantly in male subjects [OR = 9.3, (95% CI: 2.3, 26.2)] but not as strong in females [OR = 1.5, (95% CI: 0.3, 4.3)]. Younger subjects were statistically more prone to the two diseases.

CONCLUSIONS

There is a positive association between gastro-oesophageal reflux disease and irritable bowel syndrome, and their association occurs predominantly in male subjects.

Assessment of intervention measures for the 2003 SARS epidemic in Taiwan by use of a back-projection method

OBJECTIVES

To reconstruct the infection curve for the 2003 severe acute respiratory syndrome (SARS) epidemic in Taiwan and to ascertain the temporal changes in the daily number of infections that occurred during the course of the outbreak.

METHOD

Back-projection method.

RESULTS

The peaks of the epidemic correspond well with the occurrence of major infection clusters in the hospitals. The overall downward trend of the infection curve after early May corresponds well to the date (May 10) when changes in the review and classification procedure were implemented by the SARS Prevention and Extrication Committee.

CONCLUSION

The major infection control measures taken by the Taiwanese government over the course of the SARS epidemic, particularly those regarding infection control in hospitals, played a crucial role in containing the outbreak.

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.

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.

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$4343, $1771 and $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.

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.

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.

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.

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.

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.

Differing coping mechanisms, stress level and anorectal physiology in patients with functional constipation

AIM: To investigate coping mechanisms, constipation symptoms and anorectal physiology in 80 constipated subjects and 18 controls.

METHODS: Constipation was diagnosed by Rome II criteria. Coping ability and anxiety/depression were assessed by validated questionnaires. Transit time and balloon distension test were performed.

RESULTS: 34.5% patients were classified as slow transit type of constipation. The total colonic transit time (56 h vs 10 h, P < 0.0001) and rectal sensation including urge sensation (79 mL vs 63 mL, P = 0.019) and maximum tolerable volume (110 mL vs 95 mL, P = 0.03) differed in patients and controls. Constipated subjects had significantly higher anxiety and depression scores and lower SF-36 scores in all categories. They also demonstrated higher scores of ‘monitoring’ coping strategy (14 ± 6 vs 9 ± 3, P = 0.001), which correlated with the rectal distension sensation (P = 0.005), urge sensation (P=0.002), and maximum tolerable volume (P = 0.035). The less use of blunting strategy predicted slow transit constipation in both univariate (P = 0.01) and multivariate analysis (P = 0.03).

CONCLUSION: Defective or ineffective use of coping strategies may be an important etiology in functional constipation and subsequently reflected in abnormal anorectal physiology.