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Biomedical subjects

W K Fung

Publications and source records attributed to W K Fung.

8 recordsLinked to original sources
PubMed1999

Method of medians for lifetime data with Weibull models.

The Weibull family of distributions is frequently used in failure time models. The maximum likelihood estimator is very sensitive to occurrence of upper and lower outliers, especially when the hazard function is increasing. We consider the method of medians estimator for the two-parameter Weibull model. As an M-estimator, it has a bounded influence function and is highly robust against outliers. It is easy to compute as it requires solving only one equation instead of a pair of equations as for most other M-estimators. Furthermore, no assumptions or adjustments are needed for the estimator when there are some possibly censored observations at either end of the sample. About 16 per cent of the largest observations and 34 per cent of the smallest observations may be censored without affecting the calculations. We also present a simple criterion to choose between the maximum likelihood estimator and the method of medians estimator to improve on the finite-sample efficiency of the Weibull model. Robust inference on the shape parameter is also considered. The usefulness with contaminated or censored samples is illustrated by examples on three lifetime data sets. A simulation study was carried out to assess the performance of the proposed estimator and the confidence intervals of a variety of contaminated Weibull models.

Aged↗
PubMed1998

A simulation study comparing tests for the equality of coefficients of variation.

The coefficient of variation is commonly used in medical and biological sciences. In this paper, several parametric and non-parametric tests for the equality of coefficients of variation in kappa populations are reviewed. Simulation studies are conducted to compare the sizes and power of these tests. It is found that the parametric tests perform well if the data are normally distributed, but perform poorly if otherwise. The non-parametric test, however, is rather robust against the underlying distribution. An example using data of the Quality Assurance Program from the Hong Kong Medical Technology Association in Haematology and Serology is provided. The insensitivity of the non-parametric test to outliers is demonstrated.

Analysis of Variance↗
PubMed1998

Porokeratotic eccrine ostial and dermal duct naevus with dermatomal trunk involvement: literature review and report on the efficacy of laser treatment.

Porokeratotic eccrine ostial and dermal duct naevus (PEODDN) is a rare, benign hamartomatous malformation involving the eccrine sweat duct. The existence of filiform keratinous plugs that represent cornoid lamellae overlying dilated infundibula of eccrine ducts is a distinctive feature and the presence of associated abnormal dermal ducts is frequent. We report a patient with PEODDN who exhibited lesions on the left side of her chest. Cases of PEODDN reported in the literature are reviewed. Our experience in treating this patient with ultrapulsed carbon dioxide laser is also presented.

Eccrine Glands↗
PubMed1998

Amyopathic dermatomyositis in Hong Kong -- association with nasopharyngeal carcinoma.

BACKGROUND: Amyopathic dermatomyositis (ADM) is a rare variant of dermatomyositis (DM) in which there is no apparent muscle involvement at initial presentation, but clinical and laboratory evidence of myopathy may appear later. Like DM, it has a known association with malignancy. OBJECTIVE: To record the occurrence of ADM in Hong Kong during the period from January 1988 to June 1996, and to establish the types of carcinoma with which it is associated. METHODS: The records of all patients diagnosed with ADM in three major dermatology clinics in Hong Kong were retrospectively studied to confirm the diagnosis and to look for any associated malignancy at any stage of the disease. RESULTS: Between 1988 and 1996, six patients in Hong Kong (five men and one woman; mean age, 50 years) fulfilled the criteria of ADM. During a follow-up period ranging from 20 to 90 months (average, 35.6 months), none developed any evidence of myositis. Associated malignancy was found in the five male patients. There were three cases of nasopharyngeal carcinoma (NPC), one case of non-small cell carcinoma of the lung, and one case of metastatic carcinoma of the cervical lymph node of unknown primary. No carcinoma had developed in the female patient during a follow-up period of 90 months. CONCLUSIONS: There is a strong association between ADM and NPC in Hong Kong.

Adult↗
PubMed1997

Comparison of Hae-III-generated VNTR profiles of Chinese in Hong Kong and Singapore.

Some statistical analysis and experiments have been carried out on the single-locus VNTR reference databases collected separately from the Chinese in Hong Kong and Singapore to assess the issues of sample size and representativeness in the context of forensic science. We employed the bootstrap method and the Pearson chi-squared test for independence, and found that the different reference databases have very little effect in assessing the frequencies of occurrence of variable number of tandem repeats (VNTR) profiles. The results of random match probability assessment also indicate that the sample sizes studied appeared adequate to provide representative data. It has been found that a battery of four loci was enough to distinguish the 458 individuals under study.

Asian People↗
PubMed1997

Testing linkage equilibrium on allelic data between VNTR loci.

We extend Geisser and Johnson's methods and propose simple tests for linkage equilibrium of fragment lengths between VNTR loci. The tests are shown to have asymptomatically normal or chi-square null distributions. They are applied to the reference databases of Asian populations, including the Hong Kong Chinese, Singapore Chinese, Singapore Malays, and Singapore Indians. It seems that there is little linkage disequilibrium in the data.

Alleles↗
PubMed1996

Are convenience DNA samples significantly different?

In this paper, the issue of whether DNA databases collected by different convenience sampling methods are significantly different statistically is investigated. Testing the null hypothesis that the population probability or frequency distributions of DNA profiles under different sampling methods are the same is of interest in this investigation. Some statistical analyses are conducted on the single-locus VNTR databases collected from different sources by the Hong Kong Government Laboratory. The bootstrap, Monte Carlo simulation and significance tests including the Pearson's chi-squared, likelihood ratio, and Kolmogorov-Smirnov two-sample statistics are employed for testing the hypothesis. The results are promising that no probability values of the tests are smaller than 5%. In other words, there is not enough evidence to reject the null hypothesis at the 5% level, which provides more confidence for using the VNTR reference databases commonly collected by convenience sampling.

DNA↗