Biomedical subjects

Chukiat Viwatwongkasem

Publications and source records attributed to Chukiat Viwatwongkasem.

6 recordsLinked to original sources

PubMed2006

Evaluating occupational health nursing units in Bangkok textile factories: exploring the world through international occupational health programs.

The purpose of this study was to examine the service quality of nursing units in Bangkok textile factories. Descriptive survey research was combined with a qualitative design using participative observation. The sample consisted of factory managers, nurses, and employees. Data were collected between November 2001 and February 2002 using questionnaires, observation, in-depth interviews, and focus groups. Nurses' education levels and quality of design and arrangement of nursing units explained 15.7% of the variance in service quality. Furthermore, qualitative data supported clients' satisfaction with service quality, except for the tangibility of the service. These findings suggest that the quality of nursing service units could be improved by management's attention to unit design, arrangement of nursing units, and nurses' education levels. Hiring registered nurses and restructuring nursing units are recommended.

Adult↗

PubMed2005

Revisiting proportion estimators.

Proportion estimators are quite frequently used in many application areas. The conventional proportion estimator (number of events divided by sample size) encounters a number of problems when the data are sparse as will be demonstrated in various settings. The problem of estimating its variance when sample sizes become small is rarely addressed in a satisfying framework. Specifically, we have in mind applications like the weighted risk difference in multicenter trials or stratifying risk ratio estimators (to adjust for potential confounders) in epidemiological studies. It is suggested to estimate p using the parametric family p(c) and p(1 - p) using p(c)(1 - p(c)), where p(c) = (X + c)/(n + 2c). We investigate the estimation problem of choosing c > or = 0 from various perspectives including minimizing the average mean squared error of p(c), average bias and average mean squared error of p(c)(1 - p(c)). The optimal value of c for minimizing the average mean squared error of p(c) is found to be independent of n and equals c = 1. The optimal value of c for minimizing the average mean squared error of p(c)(1 - p(c)) is found to be dependent of n with limiting value c = 0.833. This might justify to use a near-optimal value of c = 1 in practice which also turns out to be beneficial when constructing confidence intervals of the form p(c)+/-1.96 square root of np(c)(1 - p(c))/(n + 2c).

Bias↗

PubMed2004

Estimating the number of drug users in Bangkok 2001: a capture-recapture approach using repeated entries in one list.

BACKGROUND: Conventionally, capture-recapture techniques involving different lists such as police or hospitals are used for quantifying populations which are difficult to count, such as illicit drug user populations. Here, a novel approach is suggested based upon repeated entries in one list, which is less dependent on matching entries from different sources as in the conventional approach. METHODS: For this purpose, a population-based study was conducted that utilizes all data on treatment episodes of drug users from all 61 health treatment centers in the Bangkok metropolitan region to estimate the size of drug use in the Bangkok metropolitan region. The data stem from the drug treatment surveillance system of the Office of the Narcotics Control Board (ONCB) and cover the period from October 1 to December 31, 2001. Based upon the frequency of treatment episodes of each patient, a count distribution arose which could be modelled well by means of a Poisson mixture model. Using this count model, an estimate for the number of unobserved drug users could be constructed. RESULTS: From 11,222 drug users found during the period, 7063 (62.9%) were heroin users, 3346 (29.8%) metamphetamine users, and the remaining 813 (7.3%) distributed under 15 drug categories, none above 1%. The study concentrated on heroin and metamphetamine users who were predominantly male (96.2% for heroin and 91.8% for metamphetamine). Metamphetamine users were younger than heroin users (22.3 years 95% CI: 22.1-22.5 vs. 30.8 years 95% CI: 30.6-31.0). By using the truncated Poisson mixture model, an estimate of the unobserved frequency of drug users with zero treatment episodes could be constructed leading to an estimate of 11,296 (95% CI: 8,964-13,628) heroin users (completeness of identification: 38.42, 95% CI: 34.03-44.04%) and 32,105 (95% CI: 24,647-39,563) metamphetamine users (completeness of identification: 9.44, 95% CI: 7.79-11.97%) for the Bangkok metropolitan region. CONCLUSIONS: The proposed model showed excellent goodness-of-fit, unspecified for drug type and also if specified for the major drug types which allowed the prediction of the unobserved number of drug users in a realistic way, avoiding artefacts due to severe matching problems when using several, different sources. The technique is also easy to implement and can be used routinely to monitor drug user populations in space and time.

Adult↗

PubMed2004

A comparison of non-iterative and iterative estimators of heterogeneity variance for the standardized mortality ratio.

This paper continues work presented in Böhning et al. (2002b, Annals of the Institute of Statistical Mathematics 54, 827-839, henceforth BMSRB) where a class of non-iterative estimators of the variance of the heterogeneity distribution for the standardized mortality ratio was discussed. Here, these estimators are further investigated by means of a simulation study. In addition, iterative estimators including the Clayton-Kaldor procedure as well as the pseudo-maximum-likelihood (PML) approach are added in the comparison. Among all candidates, the PML estimator often has the smallest mean square error, followed by the non-iterative estimator where the weights are proportional to the external expected counts. This confirms the theoretical result in BMSRB in which an asymptotic efficiency could be proved for this estimator (in the class of non-iterative estimators considered). Surprisingly, the Clayton-Kaldor iterative estimator (often recommended and used by practitioners) performed poorly with respect to the MSE. Given the widespread use of these estimators in disease mapping, medical surveillance, meta-analysis and other areas of public health, the results of this study might be of considerable interest.

Berlin↗

PubMed2003

No effect of garlic extract supplement on serum lipid levels in hypercholesterolemic subjects.

OBJECTIVE: The authors assessed the effects of an enteric-coated Thai garlic extract tablet standardized for allicin-releasing potential on serum lipid levels in hypercholesterolemic subjects. SUBJECTS AND METHOD: The authors performed a randomized, double-blind, placebo-controlled trial in 136 hypercholesterolemic subjects (cholesterol concentrations > or = 5.2 mmol/L; mean age +/- SD: 47.0 +/- 6.6 yr). All subjects were given dietary advice to lower fat intake within 4 weeks and were advised to eat normally during the study period. The subjects were randomly assigned to receive an enteric-coated Thai garlic extract tablet once daily (standardized to 1.12% allicin or 5.6 mg/tablet), or placebo after the evening meal for 12 weeks. Seventy subjects (32.9% male; mean age +/- SD and BMI of 47.0 +/- 6.6 yr and 24.6 +/- 3.3 kg/m2) received the garlic extract treatment while 66 subjects (37.9% male, mean age +/- SD and BMI of 47.0 +/- 6.0 yr and 24.3 +/- 3.4 kg/m2) received placebo. RESULTS: There were no statistically significant changes in serum total cholesterol, triglycerides, low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol after the 12-week treatment as analyzed on repeated measures by analysis of variance. In addition, no changes in plasma glucose, liver and renal functions were found. CONCLUSIONS: Treatment with an enteric garlic-coated Thai garlic extract and dietary advice did not produce any significant changes in lipid levels in subjects with hypercholesterolemia.

Adult↗

PubMed2002

Some general points in estimating heterogeneity variance with the DerSimonian-Laird estimator.

In this paper we consider estimating heterogeneity variance with the DerSimonian-Laird (DSL) estimator as typically used in meta-analysis. In its general form the DSL estimator requires inverse population-averaged study-specific variances as weights, in which case the estimator is unbiased. It has become common practice, however, to use estimates of the study-specific variances instead of their population-averaged versions. This can lead to considerable bias. Simulations illustrate these findings.

Journal Article↗